I know with us all being from different areas, the rules regarding signage changes in each county.
Out here, we have a simple rule. NO TRESPASSING. If it's posted, and you come on anyway uninvited, you take your fate in your own hands. I live pretty countrry out here, and it's commonplace to walk in someone's house and see a loaded shotgun in a rack right above the door.
We also use the honking method as we're drving upto the home. Some of the driveways out here are a mile or more long, so it's for the safety of the passengers, and any farmstock roaming free. (Horses and most cows out here will shy away from a car horn.)
I'm not certain if the No Trespassing signs would work in your case, but between that and a lock on the gate, I'm not thinking there's a Judge out there that's going to decide for the idiot in that case.