I was in St. Louis this past week for the first time. Wanting to see the arch, I headed across the street with a coworker. I was carrying my Glock 27 in my back pocket and wearing a long shirt. I didn't even think about the arch being a national monument and park until I was at the entrance to the arch with a sign staring right at me stating "NO WEAPONS." Well, my coworker was completely confused when I piped up and said I couldn't go in and would go another day. I tried to urge her to go but she opted to return to the hotel with me, complete with a very confused look as she didn't know the reason. Little did I know a park officer was right around the corner of the arch and heard the short conversation. He came out and circled around me while asking "How you doing?" I said fine as I was turning to leave. He asked if I was going in and I said maybe later. He asked "Why, are you carrying a knife or something?" Yeah, kinda like that, I have a Glock 27 in my right rear pocket. He took a somewhat defensive stance and asked all the pertinent LEO questions, like permit and such. I handed him my military ID and three concealed weapons permits. He said "Brother, I'm happy to have you here helping out. Let me escort you through so you don't have any problems.". Here I was ready for a long lecture at the very least, but to my surprise he escorted me and my guest to the metal detector and told the other officers, "He's okay....let him through (as the metal detector obviously had other ideas)." I thought about sending the NPS a great letter on the guy, but how do you do that without getting him in trouble for technically violating the law? I sure wouldn't bank on other officers in other parks being so accommodating.