There is no law on the point at all.
A GATSO is just a detection device like any other.
In fact, they can be hidden by tree branches or other furniture.
What they cannot do is obscure the speed limit in any way.
A GATSO is just a means of detection. Detection devices do not have to be advertised. Like test purchase officers in drugs cases. There wouldn't be much point if they had to be in uniform and visible.
Can I clarify anything for you?
Hi. i'm in court right now but I could call at about 1pm if that helps?
I might get a break earlier.
OK. 1pm ish.