That f-ing sucks. I'd definately try to find out who did it, so you can give them a whiping with words (I didn't say violence.)
Looks like a fire extinguisher spray pattern, but not totally sure. If you can blow it off with your breath, it shouldn't cause any damage to your paint. Hopefully it comes off easily.
I had a similar problem with the punkass kids in my old neighborhood. They would smash my mail box for no reason other than fun. That happend twice randomly. I dislike stupid people.
