Signet ring

The Doctor owned a blue signet ring.

The Doctor wore the ring in his first incarnation, but soon discarded it after his regeneration into his second incarnation, as it no longer fit him.

The ring had several special abilities. (DW: The Web Planet, The Daleks' Master Plan, The Power of the Daleks) The ring seemed to be able to facilitate hypnotism and protect the Doctor from electrical shocks. (DW: The War Machines)