The problem is that if/when this dog were to bite someone or cause harm, and if the insurance company would cover this, in most cases, the insurance company will force you to put the dog down, or otherwise deny the claim.
Putting a beware of dog sign does not absolve you from being negligent, since it is your duty to prevent harm to someone else. Pit bulls have a reputation, due to so many people out there using this breed to fight. But if you have ever watched the Dog Whisper, the main dog, "Daddy" was a pit bull and completely tame-less. I believed I read recently that Daddy died, of natural causes.
My suggestion is to find a dog that is considered tame, so you wont have to worry about it. But the key is, it is your responsibility to make sure that ANY dog that does not harm anyone else. And if you are considering a dog that you would have to put a sign up, beware of dog, then that dog is not for you.