For trucks, it varies by the trip. There is county/locality, state and federal jurisdiction.
Operators are adept at gaming the system. From Chinatown busses that use sequences of shell companies, to operators who operate out of friendly locales in a limited radius.
Difficult to work out what the law is for side visible displays is in the UK, though. Front and back ones may be limited to white or red.
I'm now wondering how camera only self driving cars are going to cope with this, too.