Well, have carried a knife openly in NC for years, checked it in the courthouse and fed building whenever I had business there, only comments ever being "nice knife." As it is, I have noticed more often than not that the security has pulled it out of the sheath. Municipal offices will put up a sign after you visit the first time, I have noted as well.
The University police requested I put it in the car once, after informing me that the student handbook was incomplete on the issue (it said that students were only allowed to have kitchen knives in their dorms - I figured, I am not in a dorm...)
I don't know what they think they're accomplishing ... if someone wanted to kill the mayor, or whatever, they're not going to be stopped by a sign.