G'day Galaxy Flyer, Welcome to Oz and our wonderful aviation security system. Regarding the "Unauthorised Weapons" signs. You will, or should, find them at every gate, door or other entrance to the airside area of a security controlled airport.
Now here's a thought. I wonder if a GA pilot with his shotgun or .22 in the back of his aeroplane can be prosecuted for not obeying the warnings? I know, I know - ignorance is no excuse blah blah blah. But that was the whole reason for the signs going up in the first place.