Exodus 28:11-12, 21

With the work of a jeweler, like the engravings of a signet, you shall engrave the two stones according to the names of the sons of Israel. You shall have them set in filigree [settings] of gold. You shall put the two stones on the [two] shoulder pieces of the ephod [of the high priest], as memorial stones for Israel; and Aaron shall bear their names on his two shoulders as a memorial before the LORD.

The [engraved] stones shall be twelve, according to the names of [the twelve tribes of] the sons of Israel; they shall be like the engravings of a signet, each with its name for the twelve tribes.