II. The Ring of the Fisherman.—The earliest mention of the Fisherman’s ring worn by the popes is in a letter of Clement IV written in 1265 to his nephew, Peter Grossi. The writer states that popes were then accustomed to seal their private letters with “the seal of the Fisherman”, whereas public documents, he adds, were distinguished by the leaden “bulls” attached (see BULLS AND BRIEFS). From the fifteenth century, however, the Fisherman's ring has been used to seal the class of papal official documents known as Briefs. The Fisherman's ring is placed by the cardinal camerlengo on the finger of a newly elected pope. It is made of gold, with a representation of St. Peter in a boat, fishing, and the name of the reigning pope around it.
BABINGTON in Dict. Christ. Antiq., s. v., 3
Maurice M. Hassett.