After you land the helicopter, look at where the two FIB agents are coming from. After they take the helicopter and the mission ends, look around the corner of the building from where they came from, and there's a black Emperor. Drive it around in the light and it seems to have a red pearlescent paint job. Unique?
This Emperor is unique. Do not respray it. I got a nickname for it, the Cadilac Fleetwood.