I live in a rough neighborhood with vandals...?

a couple months ago someone broke some windows on my house... i called the police but without witnesses they couldn't do anything... there's a camera on a pole not one block from me, to deter drug activity(don't do any good). so i put my webcam in my window and now I'M watching my own house. my question is, do i legally have to put up a sign saying the premises are under susurveillance or can i just wait til someone tries to do it again and SUE their a$$es? i just wondered if i was legally obligated to let everyone know that they were currently being recorded.