Petronella Osgood's scarf

From Tardis Wiki, the free Doctor Who reference

Petronella Osgood found a scarf which resembled one worn by the Fourth Doctor in the Grey Archive and used it to slow her bleeding after she was attacked by a Sontaran. Rather than cutting off the remaining material, she put it around her neck. (PROSE: For the Girl Who Has Everything)

Osgood continued to wear the scarf after Kate Stewart promoted her to scientific advisor. The Eleventh Doctor complimented her on it when they met and she later used it to trip up her Zygon double. (TV: The Day of the Doctor) She or the Zygon double wore the scarf whilst recording the Operation Double video. (TV: The Zygon Invasion)