Have you ever gotten autographs from people dressed up as cartoon characters? Did you think it was them? (Personally I never understood why other kids did this!) What about other people who are not famous at all - not like a local news presenter who is only a bit famous, but if a magician did a performance at my primary school, kids would try to get his autograph afterwards.
Who's autograph would you like? Or don't you care about a bit of writing, and you'd have to meet the person to make it count? Would you get the autograph of somebody very famous who you hate, so that you could sell it? (Edit- Have you asked for somebody's autograph in order to sell it?)