I disagree completely that signs have ANY legal standing whatsoever.
Can you cite a single situation where they were ever used in any prosecution?
I didn't think so.
More bad legal advice.
I cited the law right in the thread. This interpretation is backed up by Stu Weiss, Dean Greenblatt, Jim Makowski, Steve Dulan, and Steve Sudeen. Note, it puts a big burden on the prosecution that they have to prove that you knew you're not welcome beyond all reasonable doubt. One could say that they didn't see the sign.