I get the feeling the lawyers have too many fearing prosecution more than an intruder. Funny thing here is that in some places a Beware of Dog sign in the yard can be used to avoid prosecution after a dog bite. In reality there is no difference. Personally, I don't advertise anything around my home. My vehicles are always kept inside along with everything else so unless the doors are open or we are outside there is no way to tell if we are even home or not. The thing is, I don't do these things to avoid intruders or prosecution. I do things this way because I believe in taking care of what is mine. Some here would have us believe even this would be used against me by an unscrupulous prosecutor.
Where I live, an ADT or similar sign tells an intruder he has a 10 to 30 minute time window to take care of business. A sign like the one above would at least give pause to any possible intruder that was intelligent enough to read.