What type of non-permanent paint is that? I want to write a similar message when we (eventually) drive the hell out of The People's Republik of Connecticut for the last time.
That’s a tire marker paint stick (nonpermenant). I use razor blade edge to scrape it off but that does put fine scratches in your glass. You can also take it off with rubbing alcohol and a rag but that’s messy. When you communicate like this you are “pledging your fortune” (your vehicle) in the cause of free speech. Be prepared for consequences. Let them be the ones to use vulgarity.