I wonder if a more effective deterrent would be communicating that you are an abusive and neglectful dog owner. 'Beware of dog' signs communicate to me that a person is responsible and they don't want to be sued in case of an accident. If there was a sign outside that was just a silhouette of a pit bull with the words 'dog fighter' underneath, I would not want to rob that house.
"Oh no, it looks like that dog is being abused, we need to get Police and Animal Services to arrest and charge the owner and take the animal to a shelter [where it can be euthanized]" is what would likely happen in a municipality where guard dogs are put down when they bite thieves on private property with all of the mitigating factors for the dog (the dog was chained up, and could not escape, and it was in the middle of the night) and all of the aggravating factors for the thief (the area was well-secured, signed and alarmed, they could not have entered by mistake, and it was in the middle of the night).
Your common street criminal also tends to go after low-hanging fruit. A "Beware of Dog" sign and a security camera (even a fake one) will go a long way in your favor.
