What was being alluded to, I presume, is the old favourite of something being "an offensive weapon". I'm in no way legally qualified, but I believe that the basic gist of it is that anything which could reasonably potentially be carried for the purposes of inflicting harm, must be justified by being carried for a particular purpose. If someone were to be carrying a carriage key around with them in public, with no obvious cause for doing so, and were to find themselves thwacking somebody with said item, it could presumably be suggested that the item was being carried for that reason. I recall a chap giving a 'conflict avoidance' type course who'd had been consulting for a security firm. Their mobile patrols carried a decent sized and reasonably solid torch. The operatives would have this thing on their belt as standard kit, night and day. He had advised the company that should one of their staff find themselves in a tangle during daylight hours and end up using the torch for purposes of self defence, they might well be on the wrong end of an offensive weapon charge as there would be no reasonable cause for carrying it at that time. I don't know quite how watertight his thinking was, but you get the idea!
Of course, secure areas, such as a court room, may well have their own rules and prohibit items which would be permitted elsewhere. I agree that some 'security staff' can be, frankly, idiots.