Is it illegal to put a "No Entry" sign on the door?

If you put a sticker on the door, you need to judge it according to the contents of the note. If it is deemed as intimidation or slander, it is illegal. You need to judge by the abbreviation of the interview. If it means well, it is not illegal.

When we don't meet, you come to see you, but you're not there. In order to let you know that the other party has come to see you, I hope you can contact the other party when you have time and leave a notice of not meeting.