Ok...so odds are it was a neighbor but to assume they are Christian is wrong. There are a number of religions that would disagree with your statement there.

Sorry that it happened to you but it would be a lot like flying a nazi flag outside your home or posting that you want hitler as president on your lawn. You are going to make enemies with these kinds of messages. Do you have a right to make them? Yes. Are you going to have problems with others for doing it? Probably.

If you are going to get this worked up over someone taking it....probably shouldn't have it up in the first place. That or get a thicker skin about it.