Signet ring

The Doctor once owned a blue signet ring.

The Doctor wore the ring in his first incarnation, (DW: An Unearthly Child) but soon discarded it after his regeneration into his second incarnation, as it no longer fitted him. (DW: The Power of the Daleks)

The ring had several special abilities. Such as the ability to supply power to the TARDIS's Main Doors, and control a Zarbi. (DW: The Web Planet) If given the correct spectrum of light, it could un-jam a TARDIS's locking mechanism. (DW: The Daleks' Master Plan) The ring seemed to be able to facilitate hypnotism and protect the Doctor from electrical shocks. (DW: The War Machines) However, after the Doctor's first regeneration, the ring no longer seemed to have any use. (DW: The Power of the Daleks)