The Doctor's ear cuff

 was an unusual earring worn by the Thirteenth Doctor. After finally shedding the worn-out Twelfth Doctor's outfit, the Doctor chose to once again wear jewelry upon her ear (TV: The Woman Who Fell to Earth) as, according to the Second Doctor, a previous incarnation had done long ago. (PROSE: The Power of the Daleks)

Upon the Thirteenth Doctor's regeneration, the ear cuff disappeared along with the rest of her clothes, with a masculine ensemble taking their place on her successor. (TV: )

Appearance
The ear cuff features a silver star cluster worn high up on the ear in typical fashion, with a fine silver chain connecting to a more traditional  depicting clasped gold and silver hands.

Behind the scenes

 * The ear cuff was created by London-based jewelry designer Alex Monroe, inspired by Jodie Whittaker, and hand-finished replicas are available for sale from Monroe and the BBC.
 * In the regeneration scene in Twice Upon a Time and The Woman Who Fell to Earth, a slight hole in Whittaker's left ear was visible, due to her ear actually being pierced.