Visiting the license and registration building in the shop area will present you with the option of buying a new plate or customizing the plate you currently own.
A default plate is issued for any vehicle purchased in the neighborhood where a player lives. In Toreno, there is only one plate style available.
Other neighborhoods have their own plates, as well as an offering of Japanese and European plates with styles and colors corresponding to that neighborhood.
All neighborhoods offer custom/vanity plates in the style for that neighborhood.