I like The West Wing and back when I acknowledged birthdays and the like two of my friends, separately, got signed photos of Martin Sheen looking presidential [complete with certificates of authenticity]. The photos are different but the signatures are exactly the same and in the same position on the photos. I can only assume that Martin Sheen is either astoundingly precise and repetitive in his hand writing... Or someone someone used an autopen to duplicate it. There is even a hint of a pen track on the photos as if a real pen was used.
Apart from in exceptional circumstances*, I wouldn't be too bothered about a signed copy of anything, unless the person had done it specifically for me.
*It would be very cool to have a copy of LOTR or the Hobbit signed by the author.