Sifrei_mitzvot for Exodus 28:36

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.