"WHEN RATTLER SOUNDS MISSILE IS ABOUT TO FIRE"

If you know :

a/ what this means,
b/ where it is usually seen
and....
c/ have access to one of these signs, or if it's AVICOS, PM me :)

I need one for shits and giggles to stop nosey buggers.

(I can knock up a nice loud rattler - I just need a real sign)