At least in Illinois, they're euphemistically called "road-side safety inspections". I had a limo driver once get caught not wearing his seatbelt by a spotter at the beginning of a backup leading into one. The car was radioed in and, even though he put on his seat belt while in line (in his mind, well before any officer could see he wasn't wearing one), he received a citation when we finally made it to the actual inspection point.

I never even noticed he wasn't wearing one. On the rare occasion I have a driver who doesn't use it, I tell them that story.