At one time, the following warning notices appeared on one of the main squares of Prague, “Attention! Beware of pickpockets!” The local police knew that there really were a lot of pickpockets here, but they actively tore these notices down. Why?
There were a lot of tourists on this square. It was pickpockets who pasted up notices about themselves. This made their task easier. People who read the notices automatically wanted to check whether their valuables were intact. The thieves were watching them and understood where their target was.
The police found out about this trick and tore these notices down so that people couldn’t unknowingly help to rob themselves.