Ezekiel 9:3-4

And the glory of the Lord of Israel was taken up, from the cherub upon which he was, to the threshold of the house. And he called out to the man who was clothed with linen and had an instrument for writing at his waist. And the Lord said to him: "Cross through the middle of the city, in the center of Jerusalem, and seal a Tau upon the foreheads of the grieving men, who are mourning over all the abominations which are being committed in its midst."