In 17th and 18th century America, pickpocketing had become a serious problem in the major metro areas. Whenever there were large crowds around, there were skilled thieves looking to make an easy dollar by stealing from unsuspecting victims. So, in response, a campaign was launched to promote public awareness to be on the lookout. Signs were placed at street corners and gathering places, warning people that pickpockets were in the area, so be on guard. But the signs had an unfortunate side effect that inadvertently made the thieves’ larceny even easier.
The hardest job the pickpockets had was guessing which pocket the target’s valuables were in when they bumped into them, and they only had one shot to get it right. They found when the frightened public saw one of these warning signs, they would subconsciously feel for their wallets to make sure they were still there — tipping off the thieves on exactly where to strike. This was such an effective strategy that many famous pickpockets throughout history were known to put up their own warning signs around town.