A few years ago I got some books for free from a second-hand bookstore here in Zagreb, Croatia, where I live. One of those was a Real World OCaml book with a dedication from Jane Street Team to someone named Gustav. There were also some other books about functional programming given for free. I guess Gustav decided functional progamming wasn't for him, and just dumped those books to the first bookstore he could find.

Also, a few years back, I borrowed The Agebraist by Iain M. Banks from a local library and found his signature in there on the title page.