Rings may be sent from one party to another as tokens of love, distress, identification, used as signets, and so forth. Rings are perhaps the most useful pieces of jewelry for purposes of communication or of intrigue.
Rings with magical powers can be found in Arthurian romances, like Eluned’s ring that turned its wearer invisible.
Gawaine’s true identity was revealed with a ring and a piece of parchment.
See also
Ring of Dispel | The Legend of King Arthur