In the early days of motoring, bicycle patrolmen with Britain’s Automobile Association would sometimes warn AA members of nearby speed traps. In a 1910 legal case, Chief Justice Lord Alverston found this practice illegal — in effect the patrolman would be “obstructing an officer in the course of his duty.”
So AA adopted a new policy — an AA patrolman would salute any car that bore an AA badge … unless there was a speed trap nearby. The AA Handbook warned members, “It cannot be too strongly emphasised that when a patrol fails to salute, the member should stop and ask the reason why, as it is certain that the patrol has something of importance to communicate.”
The new system was used until the 1960s.