Jamieson, Fausset and Brown on Exodus 39:30

30. a writing, like to the engravings of a signet--The seal-ring worn both by ancient and modern Egyptians on the little finger of the right hand, contained, inscribed on a cornelian or other precious stone, along with the owner's name, a religious sentiment or sacred symbol, intimating that he was the servant of God, or expressive of trust in Him. And it was to this practice the inscription on the high priest alludes (compare Joh 3:33).