I have a sign from my security company. It may not be a magic shield but if I was a criminal looking for a target and saw a house with dogs, good lighting, and hedges trimmed around the windows and a Security Alarm sign, I would probably move on. I am not trying to defend against a master thief looking to break into the Gardner Museum; I am trying to deter your average low life tweeker looking for an easy score. I try to make my home appear something other than "Easy".
one of those ADT type signs just tells everyone passing by that you have stuff worth stealing.
We all have something worth stealing. What well kept middle class home doesn’t have TV's, Cameras, Computers, Possibly guns, etc. inside?