Safe paint for windows

I’m looking for some paint to write on windows (we’re headed to an rally) and I’ve heard not do good things about white shoe polish. Any ideas on what I can use? We’re taking a rental car so I want to make sure we use something that comes off easily

Any parts store will have window markers like those used by car dealers. They’re formulated to wash off completely.

Tempera colors from an art supply or school supply.

Party stores carry markers specifically for this purpose. You can get them in a variety of colors. They wash off with water. You can also buy them on line. Search for “window marker” or “glass marker”. Here’s an example of one- http://www.partycheap.com/White_Window_Marker_p/n91365.htm