Had you never spoken to him about the sign, it would not have been illegal for you to carry in there......now that he will be puting up a "legal" sign, it will be.
Actually, you're wrong. If you go back and read my original discussion string, he responded back very politely, apologizing that they'd placed the wrong sign in place, and had ordered new ones - and that he fully supported the right to carry.
So, rather than ignore or refuse to return, a polite engagement with the proper authority delivered full resolution. What's so wrong with that?