Just the fact that you are asking "Where would I stand if one of them bit someone putting their hand into my open window?" means you are aware that this might possibly happen and, therefore, you need to do something about it. I'm not sure if the police would get involved, probably not unless it was a serious injury, if your dog bit someone in this situation, but the person bitten could definitely sue you for any damages.
As to woofgang's comment "The thickness of people in regard to dogs never fails to amaze me", I would turn that around and say it's the dog owners who are usually the cause of any problems. So many dog owners seem not to realise that it's their responsibility to control their animals at all times. I can't count the number of times we, as a family, have had dogs jumping up at us when we've been out in the street or in the park or on a beach. Sometimes these dogs are bigger than our kids and it's terrifying for the child. The owners mostly seem to think it's funny - 'Oh, he's just being friendly' and 'He wont hurt them'. Maybe, maybe not, but I still don't want dogs jumping up at me.
We've also had our pet cat killed by a dog which jumped the fence into our back garden and attacked and killed the cat. Apparently, nothing could be done about it by the police or the RSPCA. The dog wasn't on a lead and was, obviously, out of control.
As I said, and as the Law says, dogs need to be kept under control.