What is an autopen and can you tell if one has been used?

As a machine replicating a person, there's some apprehension toward autopens. Is it possible to tell if it has been used in ...
KSL

Obama's signature: Is it real or is it autopenned?

WASHINGTON (AP) - It's the open secret that nobody in government wants to talk about: That cherished presidential signature that's tucked away in a scrapbook or framed for all to see might never have ...