Sketch done on the Foreword page of The Complete Bone Adventures Vol. 1, which was the original Bone trade paperback collection. I think Smith published the first two collections under this title/format before moving temporarily moving the book to Image and drastically changing the trade dress (for the better, I might add). Not that you care, but there you go.
Incidentally, this sketch and signature wasn't acquired in person, nor did I know they were in the book when I bought it. One of life's happy accidents.