Not everyone lives in a totalitarian state. In our state, "weapon" is defined by the law, not some business owner who doesn't like knives, or some random internet "expert." If it isn't a double edged dagger, dirk, brass knuckles, throwing star, etc., then it isn't classified as a weapon. Before July 1, any knife with a 4"+ blade, autos and balisongs were considered "weapons" but that changed, so now they are not legally weapons. If I see a "no weapons" sign on a private business, I check to make sure I don't have any double edged daggers, dirks, brass knuckles, etc. on my person (and since I don't even own any of those, it's an easy check). I can legally carry my Benchmade Contego past such a sign and not break any law. Our state CCW law specifies what sign carries the force of law in banning concealed guns, and a sign saying "No Weapons" doesn't cut the mustard -- according to the law. If they see it, they can ask me to leave. If I don't, they can have me cited for trespass, but that's it. If I see a properly posted business, I can choose to either leave my pistol in my vehicle or take my business and money somewhere else. It doesn't apply to knives at all.
Gov't property is a different matter. Our courthouse has the proper sign to ban CCW, and metal detectors and armed deputies to back it up (courthouse is attached to the jail). If you bring a knife in with you, they'll take it, store it in a locked drawer, and give you a slip of paper you can use to reclaim your knife when you leave. No fuss, no hard time, just "put it in here. Here's your receipt. Turn this in when you leave and get your property back. Have a nice visit!"
Our school has no policy on visitors bringing a knife into the buildings. They are properly posted for guns, so I leave it in the vehicle and carry my knife in. According to the law it is not a weapon, so I'm not doing anything illegal or wrong. If a teacher doesn't like it... tough. I'm not violating any law nor threatening anyone. And if anyone feels threatened over a fancy knife with a blue and sliver handle and purple backspacer, I'd say the problem is them, not the knife.