Repeat after me... "chalk markers". I've painted a lot of windows - starting when I was 13 or so, I painted comic book characters on the windows of our local comic book store. i used temperas with a bit of dish soap mixed in. A pain to clean off too. At Wingdoodle I always used professional window paints - they looked great, but I had to use a razor blade and ammonia to get them off. Say it again... "chalk markers" - sure you can use them on chalkboards and they look fantastic, but you can also use them on windows (and mirrors, and white boards). They are so easy to use and no mess, I let my son play too. And to clean them off? A wet paper towel. No kidding! Love 'em. They come in primary colors and fashionable ones too. If you want to paint a snowman on your window, buy the really fat white marker!! Oh, and you can use them to mark your Tupperware too. Wipes off - try that with a Sharpie!