unfortunatly yoda thats fairly common...
any sign that says "warning" is considered a problem in terms of legality, essentially stating that by saying "warning" (or "attack" you acnowledge that you have a "dangerous" animal and if someone gets hurt your liable beause you "didnt take nessicary action to contain or control the animal"
if your proptery isnt marked as private prperty no tresspassing, if something happens to someone on your land, they CAN sue, be it they fall over a log or get bitten by your dog...
however the moment you put up a no trespassing sign, it removes liability (at least this is the words of both my insurance agent and the local police)
"dog in yard" is gnerally considered a much better "warning" sign than anything that indicates said animal may be dangerous...(even if the "warning" is just to tell people not to leave the gate open, simply the use of the word warning or attack indicates a "dangerous" animal and unless your land is posted otherwise your responisbel...
stupid...ABSOLUTLY...but you better belive ill be posting no tresspassing signs around my property line...
last thing i need is for some idiot to come wandering, fall over some trash i havent managed to get cleane dup yet and sue my butt...