The AA

The AA was started in 1905 to warn drivers about police speed traps. They organised teams of cyclists to signal to drivers if they were approaching a police speed trap or a police patrol. In 1910 the AA lost a court case which meant that they were prohibited from signalling to warn drivers about police patrols so they adopted a policy of asking officers to salute members - membership was denoted by an AA badge on the car grille. If an officer did not salute it indicated that the member should stop and ask the officer why they hadn't saluted. In reality this was the signal for a speed trap or police patrol but the AA reasoned that an officer would not be taken to court for failing to salute. 

I took this when I popped down to Tesco for some milk. As I got back home the heavens opened and Noah was heading to B&Q to grab as many cubits as he could stack in his Sierra estate. I ended up sitting in the car for 5 minutes as the worst of it rolled over.