A pair of testicles attached to the rear of a car or truck used as an international symbol allowing homosexual men to identify each other.
Red or blue colors are used to indicate if the vehicle owner is a "top" or a "bottom" while other colors indicate "no preference" as well as usual, or unusual preferences.
Size of the nuts have no direct relationship to the actual size of the owner's penis and are usually misleading.
Ricky's heading down to the strip to scope out some truck nuts. He's a red so he wants blue for a night of fun.