Call for Artists, Making Money at Juried Art Fairs, Craft Shows and Festivals
We used some kind of upside down spray paint. My husband uses it on the construction sites. You hold the can upside down. We used it to mark booths in the rain. It sleeted and rained the next day. That was in November. It's still there.
I don't recommend that paint. It is too permanent. You want the crayon idea that was posted before = temporary.
Colored duct tape. It'll stick on wet cement and you can easily pull it off when done