If the chalk can be washed off, then there isn't any grounds for vandalisim charges...at least acording to the laws here. If they are going to claim that sidewalk chalk is vandalism, then they have to charge all the little kids who draw on the sidewalk with vandalisim too...just to be fair and equitable. I know that freedom of expression laws don't apply if you use foul language in a publicly noticiable place but I didn't see where they wrote anything innapropriate.

It sounds as if the police are just being total jerks. They shouldn't let personal predjudices get in the way of them doing their job.