The twelve stones corresponded to the names of the sons of Israel. Each stone was engraved like a seal with the name of one of the twelve tribes.
KJV
And the stones [were] according to the names of the children of Israel, twelve, according to their names, [like] the engravings of a signet, every one with his name, according to the twelve tribes.
ASV
And the stones were according to the names of the children of Israel, twelve, according to their names; like the engravings of a signet, every one according to his name, for the twelve tribes.