A boy has a girlfriend, but he changed the signature on the trumpet to: Cao, waiting for you. Let's see if Cao is a boy or a girl.
If it's a man, then this signature is sending a message, but there is absolutely no need to use this method. If it is a woman, it will be more meaningful and common sense. Personally, women are more likely. You need to analyze the details from the aspects of a boy's personality and style, and infer whether he is a man or a woman.