If you live in a slightly old-fashioned corner of the world, or grew up in the days of soda fountains and drive-in movies, you will have seen it: a ball-topped pole on the pavement or a revolving tube outside a shop, painted red and white, and sometimes blue as well. For many of us, this will stir images of the high-backed chairs and white-draped figures, shaving foam and old-fashioned razors of barber shops. Even after most of these shops have been replaced by more fashionable hair salons, most of them still sport the candy cane-striped pole in one form or other.

But why on earth a pole with red and white and blue stripes and a ball on top?