Exodus 28:36-38

³⁶“You shall also make a plate of pure gold and shall engrave on it, like the engravings of a seal, ‘Holy to the Lord.’ ³⁷You shall fasten it on a blue cord, and it shall be on the turban; it shall be at the front of the turban. ³⁸It shall be on Aaron’s forehead, and Aaron shall take away the iniquity of the holy things which the sons of Israel consecrate, with regard to all their holy gifts; and it shall always be on his forehead, that they may be accepted before the Lord.