Is this just a Nottingham thing?
Regularly see large - 3'x4' - bright yellow signs announcing that there is a "Police Operation in Progress. We apologise for any inconvenience" on my commute. The sign will be in place for a few days or weeks and then get moved on. Usually to another dodgy part of my commute
Now, I've never seen any trace of the Police or their operations near these signs. Which made me wonder if it was a covert operation. Which kind of defeats the object of the sign?
Can anyone enlighten me as to what these signs relate to?

