It was used almost a century ago in England to warn drivers about speed traps.
"It originated at the start of the last century as drivers started to run foul of police speed traps in which officers used a stopwatch to calculate whether or not a car was going too fast. Even then it was illegal to warn motorists about speed traps, but the AA advised its members to stop if a patrolman failed to salute, and the driver would then be given information about "road conditions" ahead."
"It originated at the start of the last century as drivers started to run foul of police speed traps in which officers used a stopwatch to calculate whether or not a car was going too fast. Even then it was illegal to warn motorists about speed traps, but the AA advised its members to stop if a patrolman failed to salute, and the driver would then be given information about "road conditions" ahead."