There's a difference between a state office building and personal property. If someone comes onto my property loudly asserting their right to be armed, it's not going to go well for them.
That has absolutely nothing to do with binding signage, though. And binding signage is not, nor has ever been required to legally kick someone off your property. It's an "Extraordinary Privilege" being provided to property owners by the state to wield the force of law against a specific class of individual. That privilege exists for absolutely nothing else.
-Mike