Hmmmm. I have thought of simular things...
"Pray the cops get to you first!"
"Beware of 6'2" 200lbs attack dog!"
"Moving targets are no problem"
(I actually had this on an old van)
"How do you know I don't have you in my sites right now?"
And have though of many other theatening slogans. But seeing that both of my rear windows got busted last week, and there was a label that said.
"Doors can not be opened from inside." Apparently the thief could not read, or did not speak or read english, and they tried anyway, and got nowhere. Good news is that it took a garden hose to wash the blood off. Bad news is that each window runs for $450. Worse... $1000 deductable!
So, I would suggest that whatever you come up with, translate into whatever localy spoken languages might be. Or international pictograph...