This does not appear to be a joke. It's a nice upper middle class street with big family homes behind spiked fences and razor wire. Other signs, for security firms, warn of "armed response". This one is refreshingly to the point.
After we stopped to take photos a lady driving a kick ass ute pulled up alongside us. "Are you tourists?"she asked. After some friendly banter about tonight's game she drove off the warning: "Keep your mobiles and your keys in your pockets around here, ya?"
Justified or not, it can't be pleasant living in a permanent state of paranoia.