Can the city do anything about the street bums wiping windshields?

Lately it seems like more and more of these people keep popping up. Just today I was on my way shopping, and I had these guys walk up and keep trying to wipe my windshield. Even though I kept saying no and turned my wipers on, they still tried to wipe. One even got mad and just put my windshield wipers standing upright. I encountered them at least 8 times today from my way to shopping and back home. This is ridiculous. Is there anything that can be done about this?