Signet rings, like we wear today, have more than likely evolved out of the cylindrical seals used by the ancient Mesopotamians as marks of authenticity and distinction in around 3500 BC. It was the ancient Egyptians that gave signet rings the recognizable form they have today, attaching seals to rings both for convenience and as a mark of individual authority.
It was during the Middle Ages, with the availability of sealing wax, that led to the development of 'intaglio' signet rings, which featured a sunken carving that could easily leave an impression in wax. At that time, it would have been hard to find a person of authority—whether it be an aristocrat or member of the clergy—who did not own a distinct signet ring. No wonder then that signet rings left an indelible mark on many official documents, and kings such as Edward II of England decreeing that all official documents must bear the king’s seal—the one on his signet.