What is Witch post?

A witch post is a local superstition where the cross of Saint Andrew is used as a hex sign on the fireplaces in Northern England, Yorkshire, and Lancashire, in order to prevent witches from flying down the chimney and entering the house to do mischief. By placing the St Andrew's cross on one of the fireplace posts or lintels, witches are thought to be prevented from entering through this opening. In this case, it is similar to the use of a witch ball, although the cross is supposed to actively prevent witches from entering, and the witch ball is supposed to passively delay or entice the witch, and perhaps entrap it.