Its unclear what they were laughing about but the Guard... I am going to say sternly stated... was

"All leaders (I think it was leaders; it could have been attendees or something along those lines) will maintain an atmosphere of silence and respect at all times."

Not sure if you have ever been there, but you just do not talk when you are there, or if you do, it is a very, very quiet whisper. I have seen them say roughly the same thing when kids are being loud so they do it to everyone and anyone. With kids, though, they typically go with more of a "this is a reminder" talk instead of the stern yelling.