In the old days, tramps and hobos were believed to operate a sophisticated coding system by leaving marks outside the homes of people they had visited. The shape of a table meant that the occupier might offer a sit-down meal; three circles, denoting coins, suggested that money might be forthcoming; a cross in a square meant a Christian lived there.
This signing technique has featured in the television series Mad Men, in an episode that contained a flashback to the past of the ad man hero Don Draper. And a few years ago, there was a craze for "warchalking", in which a mark chalked on a pavement or wall would signify where you might be able to get wi-fi access.
Now Surrey police have suggested that thieves in the Tandridge area are using a similar code. Inspector Elaine Burtenshaw described the use of the symbols as "a troubling development". She is now asking local residents to alert the police if they spot them. This time the chalking of circles on the wall is said to mean that a wealthy person lives in the house, a circle with a cross over it denotes "nothing worth stealing", while others indicate whether the resident was "nervous and afraid" or has "already been burgled".
So is there really an official Burglars' Code – or should we say the Da Pinchi Code?
"Never heard of it," says Britain's best-known burglar, Peter Scott, the author of Gentleman Thief, which recalls his days spent breaking into the homes of the rich and famous. "I find it hard to believe that burglars would bother, but then I find everything hard to believe these days." Now retired, Scott on whose life the film He Who Rides the Tiger, starring Tom Bell and Judi Dench, was based, adds: "I was always a one-man band but I can't imagine burglars leaving signs for other burglars – there isn't an association of burglars."
Still, perhaps we should take no chances. The police believe that a simple cross denotes an "easy target", so if you happen to spot one on your gatepost, surely the safest thing is to draw a neat circle round it, thus converting it effortlessly into "nothing worth stealing".