A book signing was an event where people would go to get their books signed by the author.
It was at one book reading/signing in London, where Iris Wildthyme reunited with her companion, Tom (who had become the author of a series of books about him and Iris). (AUDIO: Wildthyme at Large)
The Tenth Doctor visited Verity Newman at a signing for her book, A Journal of Impossible Things. (TV: The End of Time)