How to find the Unmarked Cruiser in Story Mode (No Missions Required): When you find it, it will be occupied by uniformed LS police officers, and upon entering the cruiser, it will be identified as 'Unmarked Cruiser' on-screen, not 'FIB Cruiser'.) To avoid confusion, this is not an FIB vehicle. (The following video titles refer to the Unmarked Cruiser as the ' FIB Unmarked Crown Vic'.
The Police Bike, on the other hand, seems to spawn in the early morning daylight hours, between 6:00 and 7:00 AM. While the Unmarked Cruiser tends to spawn between 9:00 PM and midnight, the Police Transporter seems to spawn a bit earlier, between 6:00 and 9:00 PM, which is the same time of evening that tends to conjure up the Buffalo Cruiser. Depending on the time of day in the game, the location and the technique shown in the following video can also spawn the Buffalo-based Police Cruiser, (aka: Police Cruiser 3 in the link), the Police Transporter, as well as the Police Bike. The Unmarked Cruiser is an extremely rare spawn in Story Mode and can be found in Strawberry at night at the U-shaped Los Santos Transit bus terminal, under the Olympic Freeway. ' POLICE CRUISER' trunk badge detail on Unmarked Cruiser: