The Laser Sight is only seen when looking through the scope of the Laser Sniper Rifle. It can only be seen when pointing the scope at a wall and since the player is looking through the scope where the Laser Sight is supposed to be it is useless in game.
In earlier releases of Grand Theft Auto V, Laser Sights were attachments that allowed a beam of red light that would have followed the crosshair, most likely increasing accuracy and/or range. The Lasers would have also been on hostile NOOSE, and Cops in Police Mavericks with Carbine Rifles, although this was cut.
- The idea of a Laser Sight appears in Max Payne 3, where players can equip this attachment to their weapons. However, it seem to be very "unpopular", as in this game, the laser doesn't set the aiming correctly and becomes very innacurate due to the weapon recoil, thus player usually prefers the crosshairs over this.