How to go about this issue?

One of my friend's, she stays in Nerul. In the last 1 year or so, on 3-4 ocassions, she has opened her window, and she saw an aged man, with a bit of grey hair, outside her window on the road (outside the society fence) facing towards her window and masturbating. She has decided to bring it up with the society chairman, but is there any other effective way to deal with this? As it is very unsafe, having someone do this.