An author’s signature increases the value of a book. Signed first editions, especially by famous authors, can cost an arm and a leg (the Holy Grail of the moment is a signed first edition of Harry Potter and the Philosopher’s Stone, at £8,000 to £10,000), and while there are no hard and fast rules in book valuation, a signed copy is more valuable than an identical unsigned one.
For me though, the potential value of the book is secondary; the biggest thrill from getting a signed copy is being able to come into contact with the author (or illustrator) of the book, whether directly (through the rare book signings that happen in this part of the world) or indirectly (e.g. rummaging through the bargain bins and hitting paydirt!).
