Grand Theft Auto: Liberty City Stories Easter Egg - Bickle '76 Taxi

In the game, upon entering any taxi, you can start the "Taxi Driver" missions. Upon completing 100 fares (doesn't have to be in one try, just total) you unlock a secret taxi called the Bickle '76.

Travis Bickle is main character (played by Robert De Niro) in the movie Taxi Driver, which was release in 1976. So that's where they get the name Bickle '76 and that's why they call the missions "Taxi Driver."