The law is on your side when you post a NO TRESPASSING sign. It only allows for people with legitimate business to be on your property, including the postal worker, delivery persons, meter readers and invited visitors.
It has a lot more potential to bite JWs in the @$$ than a NO SOLICITING, NO PEDDLING, NO PREACHING sign, and, in fact, the WTS has lost court cases where JWs have ignored NO TRESPASSING signs. The WTS has specifically instructed JWs to respect NO TRESPASSING signs, and its sole reason for doing so is that it does not want any financial liability for JWs who ignore these signs. With the written instructions in place, if a JW ignores these signs, they have basically been given due notice that the WTS is not going to provide legal counsel for them or stand behind them in court.
My NO SOLICITING, NO PEDDLING, NO PREACHING sign works for me in terms of keeping local JWs away. One JW phoned me and questioned me about it though. My answer was that she must have felt that she was there to preach to me when she came to the door, because the sign does not exclude social visits. Then she proceeded to go into the standard we're-so-busy-there's-just-no-time-to-visit routine. They don't bother us anymore.