If you don't have any commericial advertising on the vehicel you are driving and no need for DOT numbers most likely they won't bother you at all. But if you are running any sort of business with the vehicle you are driving, collecting big purses at the race track, writing off any of the expenses for your racing or caring equipment, cars anything else that you might be receiving compensation for, you are involved in commerce and you'll be in big doodoo if you don't have all your proper paperwork etc....
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I avoid towing my own car to the track now because of this above. I have an F250 and an open trailer and a club racer. I had no idea that having writing on the side of my car on an open trailer could get me in a jackpot.

I would think this would include any contingency decals you might be running.