It is recommended to do this ASAP since the license plate costs 5 gold. The earliest time you can earn this achievement is after you complete your first Stunt run, Destruction, and Getaway. Once your getaway is complete you can enter the garage. Once in the garage tap the Spray paint icon at the bottom of the screen. Now tap the license plate in the bottom right (It says ASPHALT on it) now type whatever you want in the blank space and once you've finished hit the enter button on your phone keyboard or tap the back button and the game will ask for 5 Gold (you start off with 8) once you pay for the license plate you should get your achievement!