I love to put numbers on the players maps on the GM layer, BUT I would love it to be locked in place and treated as a token, so I put put my GM notes about the room on it. When my players enter the room, I would just have to double-click on my room number to have all of my notes for that room. It works very well in prebought games, because the number IS a token, but it would be a pain to make 52-ish numbered token for it...