RR,
We (and other Melbourne operators) have laminated a sign to put in the window, regardless of whether the covers are on or off. That would meet the technicality of the law, inasmuch as the deterrent is plainly visible
Re using helicopters for gaol breaks: when I joined VicPol, I had a 9am start; by 9:30 I was sworn in, and at 13:00 was inside our local high security nick to advise on the feasibility of getting a B206 in and out, in order to prove a conspiracy charge.
Two days later Dave Anderson flew a JetRanger with the doors off, and was in and out in less than 40 seconds, picking up 3 Sons of God from the exercise yard (IIRC). The Governor was duly advised on how to deter future helicopter visits, as were other prisons. To this day, no prison has bothered to string wires across open spaces. In fact, our local women's prison even has a helipad
inside the facility
