Authentic
A Signature Signed By The Hand Of The Celebrity

Autopen
A Facsimile Of A Celebrities Signature Created By A Mechanical Device That Signs The Item Exactly The Same Each Time

Forgery
An Unauthorized Copy Of A Signature That Is Alleged To Be A Real Signature

Preprint
A Copy Of A Signature That Is Printed As Part Of The Photo And Not On Top. This can usually be discovered by holding a photo up to a light. A Preprinted signature will blend in with the photo and not be on top as a regular signature will

Rubber Stamp
Signature applied with ink and reproduced on a rubber stamp, usually by hand

Secretarial
A Signature signed by one or more people that handle the celebrity's fan requests