This is a list of Special Vehicles throughout the 3D Universe. Special vehicles are a type of vehicle that has unique qualities in contrast to standard ones. Such of these are unique/permanent colors and proofing against bullets, explosions, fire, and/or even collisions.
Unique trait
Code
Description
All-proof
AP
The vehicle receives no damage from anything. (BP/FP/EP/DP/MP)
Bullet-proof
BP
The vehicle receives no damage from direct hits from bullets.
Fire-proof
FP
The vehicle receives no damage from any flames or fires except when the vehicle is already burning from other forms of damage.
Explosion-proof
EP
The vehicle receives no damage from any explosions inflicted upon the vehicle.
Damage-proof
DP
The vehicle receives no damage from collisions or any form of physical damage. However, this does not protect the vehicle from melee damage if not coupled with Melee-proofing.
Melee-proof
MP
The vehicle does not receive any damage from any melee attacks (i.e. stomping or punching the vehicle). This does not protect the vehicle from collision damage if not coupled with Damage-proofing.
Tip-proof
TP
The vehicle will not catch fire when it's tipped over. This property is available in any 3D-era GTA, but can only be saved in a garage in GTA Liberty City Stories and GTA Vice City Stories.
Permanent Color
PC
The vehicle's paint job cannot be changed in a spray shop when it could otherwise.
Heavy
H
The vehicle's mass is greater than it should normally be, meaning the vehicle will lose less momentum when colliding into dynamic objects. The downside to this is that collisions will damage the vehicle more than it would normally and it reflects the same amount of your hit.
Unique Paintjob
Name of color
The vehicle's paint job is unique and cannot be obtained through spray shops or mod shops. However, the unique paint job can be painted over and lost if the player enters a spray shop with the vehicle.
Unique Handling
UH
The vehicle's handling is altered to let the player be able to cut corners and turn more quickly than normal.
Pop-Proof
PP
The vehicle's tires cannot be popped by any means.
Water-Proof
WP
The vehicle will not sink in the water where it will just blast through, falling into Blue Hell.
Double Damage
DD
The vehicle will take twice as much damage than ordinary vehicles.
Triple Damage-Stand
Unknown
The vehicle will receive a third of the ordinary damage from collision. This property is available in any 3D-era GTA, but can only be saved in a garage in GTA Liberty City Stories and GTA Vice City Stories.
Rare
R
The model of the vehicle appears only a few times during missions in the game.
Unobtainable
U
Cannot be obtained legitimately. You can only get it through trainers or Cheat Device (LCS, VCS). Some cannot be obtained without complete modifications of the game.
The Coach from The Introduction is Rare and Unobtainable (Even with Cheat Device) because all Coach's Primary color paints the luggage doors on the bottom of it and as you can see in the cutscene, the bottom is all-white.
Special thanks to jam8tone , TheGlitcher123100 , Gabybosskingofspeed, DGTZ1982 and Slotered for finding all vehicles.