Exodus 28:35-37

35It must be worn by Aaron whenever he ministers. The sound will be heard when he goes into the holy place before Adonai and when he comes out, so that he does not die.

36“Also you are to make a plate of pure gold and engrave on it, like the engravings of a seal, ‘HOLY TO Adonai.’

37Attach it with a violet cord onto the turban, on the front of the turban.