I usually do the same.
In 2006 I had to visit a Revol (I think?) cell phone store to get some tech help on my wife's phone. They had a rather ominous sign on the door about "Absolutely no firearms allowed". This was in Indiana mind you. I went in anyway and got my business done. Then I asked to see the manager. Turns out the guy that helped me was the manager. I asked about the sign. It was corporate policy according to "Tim." I asked about police officers and licensed to carry citizens. Tim said, "It was more for would be criminals." Without me saying a word, Tim immediately realized just how stupid that was and said, "I guess that doesn't make much sense does it." It was as if he had never really heard how stupid that sounded until he himself had to say it out loud. I smiled and left without him ever realized I was carrying concealed. The sign was gone the next time I happened to drive by the store.
Your interaction with the manager revealed that most people don’t like being made to look or feel stupid, especially in a work environment. Two thumbs up to you for your gentle nudge for him to see the light!!