I probably wouldn't respond this way, but: if I see you touching my car, my personal property, and you're not wearing a law enforcement uniform, it would be well within my right to respond as if you're stealing or vandalizing my car. I can't speak to SF, but in many areas, when the police respond to the physical altercation, they'd be asking me if I want to press charges.
As annoying as it can be to come out and find someone has placed a flyer on my car, I very, very, seriously, highly doubt that I would NOT be charged for assault if I was to beat them up for it. But I'm willing to look at evidence in the contrary.
