Autograph

An autograph was a type of signature, usually written by a famous person to an admirer.

Arriving at the Space Station Camera for a meeting with Joinson Dastari, the Second Doctor explained to his companion Jamie McCrimmon that he was "slipping in quietly" to avoid the "commotion" that would be caused should they have been discovered by the "most brilliant scientists in the universe" who had been assembled there; the Doctor anticipated that they would all be "scrambling around wanting [his] autograph." (TV: The Two Doctors)

The Fourth Doctor attended the recording of the song Do They Know It's Christmas?, which he saw as a great opportunity to collect autographs. (PROSE: The Clanging Chimes of Doom)

The Fourth Doctor himself was once asked for an autograph at a restaurant, being mistaken for a Suitor. (PROSE: Suitors Inc.)

The Fifth Doctor was once asked for his autograph by Maven, a Time Lord and agent of the Celestial Preservation Agency who had travelled back from a future period of Gallifreyan history. (AUDIO: Omega)

The Sixth Doctor got Evelyn Smythe to sign his copy of her book The Merlin of Mortlake: The Life and Talents of Dr John Dee before she had even written it. (PROSE: Mortlake)

Ace got an autograph from jazz musician Courtney Pine when she attended one of his performances, with the Seventh Doctor, on 23 November 1988. (TV: Silver Nemesis)

When the Seventh Doctor was trapped by the Monk on the unnamed ice planet where the Monk himself had once been trapped, he escaped using a piece of the Monk's TARDIS, which was disguised as Danny Pain's autograph. (PROSE: No Future)

While staying at The Elephant in 1599, William Shakespeare assumed that the Tenth Doctor had entered his room to ask for an autograph and preemptively rejected such a request. (TV: The Shakespeare Code)

During her time as a model for Petrichor, Amy Pond gave an autograph to a young fan called Ellie. (TV: Closing Time)

The Eleventh Doctor signed autographs for various Doctor Who fans at a convention when he entered a parallel universe. One of the fans, Gina, originally wanted Matt Smith's autograph instead. (COMIC: The Girl Who Loved Doctor Who)

Zzagnar autographed copies of his comic book, Zz-Men, at Hypercon circa 2015. (COMIC: Give Free of Die)

The Thirteenth Doctor asked actor Errol Flynn for his autograph when she met him in Follyrood. (COMIC: The Greatest Movie Never Made)

In 1968, George Lowcock got an autograph from Edmund Trevithick. (PROSE: Nightshade)

Behind the scenes
Introduction, one of the comic stories in The Doctor Who Fun Book that are not considered valid sources on this Wiki, focused on Peter Davison being asked for... Tom Baker's autograph by an enthusiastic Doctor Who fan holding an autograph notebook.