In the missions done for Gerald McReary while he is in prison, a chart can be seen behind Gerald during the cutscenes for the mission. There are several names written on it, all of which are puns, including "Isaac Hunt" (I's a cunt), "Seymour Fani" (see more fanny), "Richard Head" (dick head), and "Phil Mcreavis" (fill my crevice).
Within the Statue of Happiness is a giant beating heart, supposedly the "Heart of Liberty City." In GTA IV, access into the area is only achievable via an entrance marked by a "No Hidden Content This Way" sign at the upper level of the the statue's pedestal, which can only be reached by helicopter. Once inside the pedestal, the player must scale a ladder up to the midsection of the statue, where the heart is located. It can be shot at, but nothing happens. In Ballad of Gay Tony if you drink too much you will respawn at random locations, one of which may be the Heart of Liberty City.
You can access the roof of Playboy X's penthouse suite by jumping on a power box to the right of the patio door. However the player must jump from a certain point of the box to grab onto the roof, jumping too close to the edge oddly will not allow the player to make it onto the roof. It is possible for footprints to appear on top of the box, indicating exactly where Niko's feet must be to make the jump. It has also been observed that these footprints will turn to blood spatters after shooting someone, and will only reappear when you are standing on the box and are being shot at, thus drawing your own blood.
The lake in Middle Park resembles the shape of an alien. This can easily be noticed on the map or from the air in a helicopter.
In the Broker Safehouse there is a picture of Roman and an unnamed woman. Notice that he looks almost completely different.
At the Firefly Projects, there is a park with a swing set. If you drive backwards (or forwards with some vehicles such as a Voodoo) onto it, the swing set will catapult the vehicle high in the air. This is likely a bug in the game's physics simulation. See Swing Glitch article for more details.
While driving the Mr. Tasty, you can trigger songs to play by clicking the horn. One of these songs is the theme song of GTA IV. While this song is playing, call ZiT and they will text you back with "ZiT! Spotted GTA IV Theme". This is a cheat that gives the player health, armor and ammo, but also disables some achievements.
At all TW@ internet cafes, behind the cashier's desk, and also inside various vehicle dealerships, the screen of the Kakagawa Power Ultra 3000 Pro photocopier reads: ERROR Unleash ninja guru lol. This can only be seen through the scope of a Sniper Rifle.
If you take a helicopter ride from Brucie Kibbutz, or you go for a helitour, there's an unsettling warning message about the helicopter inside the cockpit that you can see if you look in first person mode that says "This helicopter might crash but we really don't care if it does, refer to flight manual for help."
In The Lost and the Damned, the dash of the Rhapsody has a sticker of Wayne and Garth from the movie Wayne's World, which famously features the song Bohemian Rhapsody.
While playing multiplayer, some of the TVs in safehouses and the TV in the MeTV building, show the game's pause menu without the map.
If the player scopes the night sky with a sniper rifle on a clear night, they will find some galaxies (a false representation, as galaxies themselves cannot be seen without a telescope), stars and a flying thumb, in the thumbs up position.
Behind an old, rundown mansion in Westdyke, Alderney at the end of the dirt roads, there is the hidden, extremely rare Sultan RS parked in some bushes. This is practically the only way to find the car ingame. The only other way to obtain it is if the game has it stored in the temporary memory (perhaps because one appeared in one of Brucie's Races), and automatically spawns it parked or driving around the streets.
On the west side of Happiness Island, there is a random spawn that can be a car. This is unusual as there is no way a vehicle can be brought on to the island unless unloaded by a ship.
Normally hostile pedestrians flee. Go into any strip club and either shoot it up or spend some time with a stripper. Then go to areas where there are gang members that will become hostile if they are bumped. Punch them and they will run away. Drivers that normally would get out and try to hurt you if you punch or hit their car will also flee. This only has a temporary effect.
There are rumours of a "mythical creature" called "Ratman". Supposedly, he is found wandering around the subways. Some report of his sightings being simply a homeless man, while others report him being a half-human, half-rat creature, hence the name. This has not been confirmed in any way.
References to previous games
On the staircases in most apartment blocks in the game, you may spot some graffiti referring to past protagonists set in GTA III canon (Claude, Tommy, Carl (CJ), Toni, and Vic), that suggests they have passed away, though it is likely metaphorical as GTA III canon is over so they won't be seen again. The only onscreen death of a protagonist so far is Victor Vance. The graffiti is intended to serve as "a little joke for fans of the series", as a different design approach to GTA IV meant the games' timeline could only inherit various fictional brand names and certain radio personalities; it is, however, no indication as to whether or not GTA III canon has been retired.
There are signs scattered throughout Liberty City that say "Hot Coffee Shop", clearly a reference to the Hot Coffee sexual content and controversy from GTA San Andreas
There is a Sprunk manufacturing plant in Alderney and a vending machine at Romans taxi depot. Sprunk was featured in GTA Vice City, GTA: San Andreas, and Manhunt. It has returned to GTA IV with a brand new look. Also notice that "Sprunk" is a mix of the words "Sprite" and "Spunk". The sign outside the factory is very similar to a sign for Pepsi-Cola that appears in the film "The Great Gatsby."
Similarly, footage of the Vinewood sign from GTA San Andreas is used for another TV ad; it is recognizably San Andreas animation due to the transmission tower visible right behind it, which was also in the earlier game.
The Securicars are owned by the Gruppe Sechs security firm (also seen in IGTA III and Vice City), although in GTA IV the name is rendered as "Gruppe 6". "Sechs" is the German word for Six and "Gruppe" means group.
In the bars are postcards featuring Vice City. Vice City is also advertised in airfare billboards near the airport.
Niko can receive an email from Chiliad8888, which calls the recipient "Pilgrim", makes many spiritually- and philosophically-charged (and anti-government) comments, ends with "Feel the Truth, Live the Freedom", and links to whattheydonotwantyoutoknow.com. On this website there is a discussion topic titled, "Jump to a new level of Spirituality" posted by "Trooth". This discussion thread includes more philosophical thoughts, mentions Peyote, and provides a map of the Unique Stunt Jumps in Liberty City. "Chiliad" was also the name of a location in San Andreas (the highest mountain, in the southwestern wilderness). These clues suggest that the author of the email and discussion topic is The Truth, a character from GTA San Andreas.
On Happiness Island, in front of the entrance to the statue, it is possible to find a street-artist's easel/display stand with several pictures. These pictures are all concept works of many previous GTA characters. The easel can also be seen in south-central Algonquin, very close to where Hossan's random encounter takes place and in front of the The Libertonian.
A billboard outside the Algonquin safehouse shows a man who is said to be CJ, drinking wine.
During a multiplayer race in GTA IV if the player equips a certain Female face (possibly 2) then hits a car in traffic or another player's car while pressing the talk button (PS3 or Xbox), the character will sometimes exclaim,"This isn't San Andreas you hippie, DRIVE!"
One of the in-game radio advertisements is for an online service called Babiesovernight.com. The tagline at the end and the background music are evocative of the commercial in GTA III for Petsovernight.com.
References to other games
In the amusement park in Broker there are blue/purple Hippo Statues, just like the ones from Manhunt.
Numerous references are made to Carcer City, the setting of Manhunt.
The achievement/trophy for completing all the most wanted side missions is called Manhunt.
On the TV channel Weazel, there is an animated TV show called Republican Space Rangers, which spoofs the Halo series, as it features space marines wearing a green armor that resembles the MJOLNIR armor as seen in Halo. In one scene, the Rangers fly their spaceship through a ring that resembles a HALO ring.
Certain random female NPCs will, upon being pushed, exclaim "Well excuse me dorkwad!", a possible reference to the Legend of Zelda cartoon.
In the Lure Dealer room there is Gordon Freeman's crowbar from the Half-Life series.
A pedestrian bearing an uncanny resemblance to Jimmy Hopkins, the protagonist of Bully, can be seen roaming the streets of Liberty City. He is even wearing a Bullworth Academy vest. He is, however, much more aged but does have a similar buzz cut hair style.
On the wall in the arcade place in Chinatown, there are several sprites on the wall resembling those of old games. One of the sprites is a blond man, with a long mustache and plumber-like black clothes. The sprite resembles Super Mario from the Super Mario Brothers series.
In Cluckin' Bell restaurants, near the back of the store, there's an action figure of a man in a martial arts position wearing a chicken hat; printed on the glass is "Cluck Norris," a reference to film/television star and martial artist Chuck Norris.
In the second apartment you unlock (Located in Bohan) there are books sitting on a table near the TV. Shoot one of the books and there is another underneath that says it was written by Nuck Chorris. This is also a reference to Chuck Norris.
Avenues running north-south (vertically) in Algonquin are named alphabetically after American cities. "A" is at the eastern side of Algonquin; "G" at the western. The names, in order, are Albany, Bismarck, Columbus, Denver, Exeter, Frankfort, Galveston. Denver and Exeter run concurrently ("Denver-Exeter Ave.") south of Middle Park into Star Junction.
Streets running east-to-west (horizontally) in Algonquin are named alphabetically after different types of minerals. "A" is at the southern end of Algonquin; "X" at the northern end. The names in order are Amethyst, Barium, Calcium, Diamond, Emerald, Feldspar, Garnet, Hematite, Iron, Jade, Kunzite, Lorimar, Manganese, Nickel, Obsidian, Pyrite, Quartz, Ruby, Silicon, Topaz, Uranium, Vauxite, Wardite, Xenotime.
Many street names in Bohan are named after prisons -- Leavenworth Ave, Alcatraz Ave, Sing Sing Ave, Guantanamo Ave, Attica Ave, San Quentin Ave, Folsom Way (best known from "Folsom Prison Blues" by Johnny Cash), Rykers Ave (named after the Rikers Island prison on the East River of New York City), and Joliet Street (Joliet, Illinois).
In South Alderney, the street names reflect (mostly antiquated) military terms -- Musketeer, Grenadier, Chariot, Phalanx etc.
In Broker, roads running North-South are named after Native American tribes -- Iroquois, Oneida, Mohawk, Onondaga etc.
In Broker there are the street names "Cassidy" and "Sundance", a reference to the outlaws, Butch Cassidy and the Sundance Kid.
The Beatles: Broker contains the streets "Ringo St" and "Starr St", both references to the Beatles member Ringo Starr. In Dukes there's a Harrison St., probably a reference to George Harrison, and the northwest section of Liberty City contains the Long John Ave, name that John Lennon used at the beginning of his career. Paul McCartney references are not found yet. Also on the side of buses, there is a small ribbon saying "here, there and everywhere" which is a reference to the Beatles song "Here, there and everywhere".
In Alderney, some streets are named after cult leaders: Hubbard St., Applewhite St., Koresh Square
Some streets are named after tools -- Jackhammer, Plumbbob, Tinderbox, Drill.
Some streets are named after insects -- Caterpillar, Worm, Butterfly.
Some streets are named after foods -- Onion, Asparagus, Chive.
Some streets are named after colonial Settlements -- Yorktown, Delaware.
Some streets are named after famous surnames -- Harrison, Hancock, Livingston.
Some streets are named after nuclear tests -- Plumbbob, Emery, Niblick, Ivy, Hardtack, and Trinity.
Some streets are named after inventors -- Edison, Schneider, Moog, Drebbel, Farnsworth, Cockerell.
The street in Northwood named Astoria's full name is Astoria Place. This could possibly be a take on Astor Place in the Lower East Side.
On the stairway leading to the sea at Meadow Hills there is a 'Banksy-esque' style graffiti piece.
There is a Liberty Tree article that talks about urban myths in Liberty City. This could be referring to the myths that were created around San Andreas.
An online article on Liberty Tree's website, an Air Sol flight has 212 passengers on board, 212 a reference to the area code in New York City.
In Willis, there is a shop called Al's Furniture. This is a reference to Italian-American gangster Al Capone, who was officially the owner of a furniture shop.
The fact that a secretive government body operates out of a paper factory may be a reference to the TV show Heroes. A secretive organization in that show also uses a paper factory as a cover and much of the action takes place in New York.
The viral video, 2 Girls 1 Cup, is indirectly referenced to numerous times on the radio.
Also in the mission, Final Interview, the laywer Tom Goldberg, which Niko has to kill on orders of Francis McReary, is supposedly based on a real-life disbarred lawyer, Jack Thompson, who is an activist against violent video games for minors and is a well noble arch-enemy of Rockstar. One of the lines Goldberg says when Niko pulls out a gun during the interview is a real-life reference to one of Thompson's famous lines against violent shooting games that are "murder simulators" is "Guns don't kill people, video games do!"
There are a lot of people complaining that they have to smoke outside. This is a reference to New York City, where you can't smoke inside either.
On many alley walls there is grafitti that says 'Cope' a famous grafitti artist in the real world.
When you wound a cop sometimes they will shout "I'm gonna be okay!", referring to Reservoir Dogs, when Mr. Orange is shot in the abdomen and is screaming in delirium.
If you go on a Heli Ride with Brucie , and if you go to the Rotterdam Tower, Brucie might say "If I was that big chimp, I would climb it too." This is a referrence to King Kong
As with previous games, the number 69 is used on various occasions in Liberty City, one such instance being on the Fire Trucks. 69 is a reference to the sexual position of the same name.
The outside sign for the Memory Lanes bowling alley depicts a bowling pin with two bowling balls on either side of it. Inside, however, the sign is only a neon outline, and resembles a crude drawing of male sex organs.
In many spots around Liberty City, there is rubble on the ground; in some of this rubble, you can see a purple dildo sticking out. This is the same dildo used as a weapon in GTA San Andreas.
Looking at the golf courses carefully from a height reveals that they are penis-shaped.
A brand of beer in the game is called "Dusche Gold". "Dusche" is German for "shower", so it translates into "shower gold", a reference to "golden shower", the act of urinating on someone.
Another beer brand is named "Pißwasser", "wasser" being German for "water" and "ß" is a German letter for "ss". An advertisement for Pißwasser shows a woman with the bottle in her mouth as if in an act of fellatio.
The logo for AutoEroticar is a car resembling a penis. The name also has the word "Erotic", saying that the cars are going to give you an erection.
In BOABO, Broker, there is a building called, "The Clocktower" and it has a digital clock that displays the in-game time. When driving on the Algonquin Bridge at night, leaving Algonquin, you can see the word CLOCKTOWER lit up except the "L" is not lit and it says "COCKTOWER".
In Middle Park there is a monument that resembles male genitalia. According to a plaque at its base, it is called "Le Knobeliske" and was presented to Liberty City by C. Shutchomouf in 2007.
In hospitals, there are posters about sex.
In Florian's (Bernie's) apartment, in his family room, there is a picture of a flower that represents the male genitals.
Meals at Cluckin' Bell prefer to use the word "cock" instead of "chicken".
Another thing in Cluckin' Bell is the names above the restrooms. The male restroom says "Cocks" above it and the female restroom says "Chicks" above it.
The series of internet cafes known as Tw@, is a clear refference to the female vagina. When the "@" is pronounced as "at".
One of the restaurants is called "Viendemorte", which sounds exactly like "viande morte". It means "dead meat" in French.