Exodus 28:36-38

And you shall make a plate of pure gold and engrave on it, like the engravings of a signet, holy to the lord. 37 You shall fasten it on the front of the turban with a blue cord. 38 It shall be upon Aaron’s forehead, that Aaron may take upon himself and bear [any] iniquity [connected with] the holy things which the Israelites shall give and dedicate; and it shall always be upon his forehead, that they may be accepted before the Lord [in the priest’s person]