In 12 years of driving my speedster, I've never been stopped for any reason. In Ma. a front plat is required for your annual safety inspection . It gets installed , and comes right off after that. I keep the front plate in the trunk mounted on a bracket that I could put on in 2 min. if needed. I always smile and wave to the cops and they usually wave right back.
If they ever ask me about it , I would apologize profusely and explain that it was removed for a car show.
I think the police have bigger fish to fry and my red speedster doesn't look like the type of car that a criminal would use to sneak around in.