AA (Automobile Association) patrol men used to salute members sporting an AA badge on the front of their cars.
If the patrol man didn't salute, the driver knew there was a policeman ahead so slowed down.
Incidentally, the AA men then rode motorcycle combinations - vans came later:
http://www.theaa.com/motoring_advice/aa-heritage-vehicles/bsa-m20-and-m21.html
http://www.oldclassiccar.co.uk/aa-motorcycle.htm
http://www.timesonline.co.uk/tol/archive/article4114540.ece?slideshowPopup=true&articleId=4114540§ionName=PhotoGalleries
Now gone full-circle (scroll down to the bottom):
http://www.twistngo.com/news-twg.htm
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Mike - Riding on the right - riding for pleasure!
'09 Silverwing 600 - 'The Winged Express' - Delta Blue, ABS, Heated Grips, Givi Airflow Screen, Utopia rider's backrest, Givi pillion backrest & E52 Topbox, Cortech Super Mini Tank Bag as a tunnel-bag, Starcom Digital Comms System.
www.x9ownersclub.co.uk - for all Maxi-Riders who want to RIDE!
"All that is necessary for the triumph of evil is that good men do nothing."
Edmund Burke