. . . you know, one that actually recognized private property rights, the natural progression illustrated below would be perfectly acceptable.
A simple statement, easily understood, establishing a clear boundary saying, “Not yours. Stay out.”
If a trespasser were to proceed, then a second warning might justifiably be issued by an exceedingly patient and forbearing landowner:
If that failed to deter a malefactor, then *sigh*. . .
OK, MORE than excessively generous, kind and gentle landowners might include, between #2 and #3 (or #1 and #2), a sign stating,
Fence and “No Trespassing” Signs
Security/Surveillance System
Guard Dogs
Armed Response
For clearance to enter the property try calling 1-800-UGO-AWAY
Is “No Trespassing” Clear Now?