Exodus 28:36-38

“You shall also make a plate of pure gold and engrave on it, like the engraving of a signet: HOLINESS TO THE LORD. And you shall put it on a blue cord, that it may be on the turban; it shall be on the front of the turban. So it shall be on Aaron’s forehead, that Aaron may bear the iniquity of the holy things which the children of Israel hallow in all their holy gifts; and it shall always be on his forehead, that they may be accepted before the LORD.