In Missouri, the sign really only indicates the building occupants desire that no weapons come in. If noticed, you may be told to leave and you may return w/o your weapon. If you don't follow this instruction, you're trespassing. The local Social Security office had an illegal sign posted on their door. When I went in (left my pistol in the car) with an empty holster, the guard got all fuzzed up. I informed him of the nonstandard signage and suggested if he intended to enforce it, he'd better get a legal notice posted. He was still hyped so I got my phone out and started taking pics of the sign. Next time I had to go to SS office, there was a proper sign and a different guard. Funny how the SS office needs an armed guard at the door.