IIRC.....BAD ADVICE
Current legal scholars recommend you NOT to put "beware of dog" signs up since, IF your dog bites someone, the warning sign indicates that you KNEW of a potential of future dog aggression and the victim will wipe the court with your good intentions and bank account. Shrug...some areas of the countries are different, but sounds legit.
Better idea: Fence with "no trespassing" and "private property" sign clearly visible. I don't know what alternative to warn people of a dog on your property would be, but I was advised on my farm to have "no trespassing, no hunting, private property, and no soliciting" signs posted. Oh, and your doormat should say this:
I like it, and add grounds patrolled by guard dogs and trespassers will be shot. However, I bet the last item is probably illegal in much of the formerly free USA.