What is a piece of red cloth above the main entrance?

In fact, the person who hangs red cloth on the door frame has several viewpoints and functions:

First, the host is happy with his son, and the woman is pregnant, so red cloth is hung on the door. First, it is festive; The second is to tell tourists to keep quiet.

Second, if there are streets in front of the door, there may be something not peaceful or catastrophic. The ancients often used red cloth or round mirrors to solve it.

Third, the landlord hangs red cloth, which is intended to drive away tourists' filth and ensure safety.