If an author is doing a tour of signing sessions, chances are there will be a LOT of signed copies about, so the premium is going to be limited, unless (a) the author drops down dead shortly afterwards or (b) you are prepared to put the books aside as an 'investment' for a year or ten. At the extreme, there is the case of Peter Hamilton's 'Naked God' sf novel, where the publisher craftily sent all the first printing to shops where he would be signing..so an UNsigned copy is actually going to be the rarity (!) But at least you can guarantee (and say so in your description) that the signature is genuine. | 
