Spoilers follow! You have been warned…
What I saw is really intriguing… the Doctor is at a book signing of A Journal of Impossible Things – which appears to have been published as a novel by “Verity Newman” (a name taken from Verity Lambert, the first producer of Doctor Who, and Sydney Newman, one of its creators). There were banners up with a cover showing the fob watch, very similar to Pullman’s Northern Lights cover.
What’s more, Verity Newman is played by none other than Jessica Hynes (nee Stevenson), who played Joan Redfern in Human Nature!
It’s clearly the present day, so either Joan has time-travelled and become a novelist, or this might be Joan’s granddaughter, who inherited the Doctor’s journal, and has turned it into a novel. Very intriguing!
Edited to add: I wandered back down, to find that filming had finished and was packing up. As I walked past the entrance to the bookshop, Jessica Hynes walked out, right next to me, almost bumped into her! There was an odd moment as I recognised her, she saw I recognised her, and I went “urk!” As she went to the car I said, “I really loved Spaced! Erm… that’s a bit of a rubbish thing to say, but it’s all I can think of at the moment”. But complimenting someone on their work is never rubbish, and she smiled and waved, which was nice. I hope I didn’t scare her too much!