I once had the opportunity for a police officer to explain to me that you are not allowed to add or have anything cover your license plate. Anything meant clear plastic, a license frame that covers any of the writing or dirt as in my case. It was a dirt bike the whole thing was covered including me. He told me that I need to clean off the platebefore I enter the road way, that way an officer could tell that the bike was legally registered for road use. He spent ten minutes lecturing me, I though for sure he wasn't going to write me up after being so helpful on all the rules. When he started to write it, I asked if that was a points ticket, he said "No.", I laughed, He didn't. He told me he was going to follow me and if I dropped any dirt he would write me up for littering. I told him fine, made a right hand turn and disappeared into the woods.