There used to be something similar in the UK IIRC - the traffic police nicknamed themselves "black rats". If you had a sticker of the black rat mascot/logo on

There used to be something similar in the UK IIRC - the traffic police nicknamed themselves "black rats". If you had a sticker of the black rat mascot/logo on the back of your car then you were either a traffic officer, or someone close to them (wife/husband/etc) and a wink and a nod an you were on your way. I don't think it was a deliberate "get out of jail" move - just more of a "Oh you have a sticker for my unit's mascot on your car!" recognition type thing. I think it kinda stopped when they started giving away the stickers on "enthusiast" car/motorbike magazines etc