Exodus 28:36-38 NIV

36 “Make a plate of pure gold and engrave on it as on a seal: HOLY TO THE LORD.

References for Exodus 28:36

37 Fasten a blue cord to it to attach it to the turban; it is to be on the front of the turban.
38 It will be on Aaron’s forehead, and he will bear the guilt involved in the sacred gifts the Israelites consecrate, whatever their gifts may be. It will be on Aaron’s forehead continually so that they will be acceptable to the LORD.