My favorite is, and always has been:
NO TRESPASSING
All violators will be shot.
All survivors will be shot again.
Ha!
I saw something similar done as a cartoon on another site...
so I grabbed one of my own pics of my Springfield (with Zombie ammo!) and made one of those fake "demotivational" posters out of it;
lol
Aren't warning shots against the law anyhow?