Why do supermarkets post "I am a thief" notes to the elderly?

Even if the old man is really a thief, it is wrong to do so, and it is also a kind of personality of Lu. An act that denigrates the dignity of the other party. This behavior is not desirable. If the old man is not a thief, then this is definitely an insult. He committed the crime of libel. It is also illegal.