Exodus 28:11-12, 21

As a jeweler engraves signets, so shall you engrave the two stones with the names of the sons of Israel. You shall enclose them in settings of gold filigree. And you shall set the two stones on the shoulder pieces of the ephod, as stones of remembrance for the sons of Israel. And Aaron shall bear their names before the LORD on his two shoulders for remembrance.

There shall be twelve stones with their names according to the names of the sons of Israel. They shall be like signets, each engraved with its name, for the twelve tribes.