וְעָשִׂ֥יתָ צִּ֖יץ זָהָ֣ב טָה֑וֹר וּפִתַּחְתָּ֤ עָלָיו֙ פִּתּוּחֵ֣י חֹתָ֔ם קֹ֖דֶשׁ לַֽיהוָֽה׃
And thou shalt make a plate of pure gold, and engrave upon it, like the engravings of a signet: HOLY TO THE LORD.
Read kabbalistic (mystical) interpretation of Exodus 28:36: and classical mystical sources.