"No guns" signs ?

I have recently seen "No Guns" signs on Post office entrance doors and a few business's. Is this a legal ban or just a suggested request? I just ignore them because I have read the Constitution and have a CCP.

Try walking in any Federal property with your gun displayed, you want like it, no matter what your rights are.
I had a Field Tech staying at a Indian Casino/Hotel here in Oklahoma, on Federal land, he forgot & laid his pistol on the check-out desk whith his laptop.
The next thing he knew, he was on the ground being hand-cuffed.

Luckly, calmer heads prevailed.
He explained that the door locks on his Service truck were broke & he had been keeping his gun in his room safe.
They confirmed his story, returned his gun & give him a lecture.

Our company also posts "No Guns Allowed" at all branches, we have 8 in 6 states.