Suppose someone wrote a note to their mayor on a brick wall, not using profanity, drawing anything remotely vulgar, or making any sort of threat. More of a call to action.
Is it considered graffiti if chalk, which would wash away the next time the rain came, were used?
Hypothetically… 
Probably depends on the mood of the cop who catches you in the act. I recall a few years back when I was going to school at UW-Madison, some folks got cited for chalking the sidewalks during some sort of school election campaign. There was a bit of outrage in the school papers, and I think the tickets got thrown out in the end, but the fact that the “graffiti” wasn’t permanent didn’t stop the cops from issuing the ticket in the first place.
I can assure you, at least in sacramento, that the cops will be less than happy with you when you play a game of tic-tac-toe on the back of an empty building with chalk.
Really. I’ve told the story before…
Well then link my good sir! Link for the love of Og!
And I hear from a few friends that businesses don’t like it when you chalk up thier sidewalks.
Yes. But since graffiti charges often include the cost of covering it up/removing it- then your fine would be less.
The bit about “which would wash away the next time the rain came” is rather specious, unless you expect rain the next day. After all- paint will also wear away given enough time.
The Hopscotchers Association of America is going to be very upset.