Your guess is as good as mine. The designated ORV parks for sure, unclear on plain old DNR land and not sure what other places would require it.
From what I gather, only DNR land requires a street plated bike to have something in addition to the road license plate. It sounds like that may either be a Discover Pass or the ORV sticker/plate. That's pretty confusing if true.
At least you don't have to worry about a spark arrestor, that is an even worse nightmare.