Exodus 28:11-12, 21

As a jeweler engraves a signet, you shall engrave the two stones according to the names of the sons of Israel; you shall set them in filigree settings of gold. You shall put the two stones on the shoulder pieces of the ephod, as stones of memorial for the sons of Israel, and Aaron shall bear their names before the LORD on his two shoulders for a memorial.

The stones shall be according to the names of the sons of Israel: twelve, according to their names; they shall be like the engravings of a seal, each according to his name for the twelve tribes.