I recently started searching that highly ethical website, Ebay, for GA listed items, and I am amazed at how many different signatures they manage to butcher. Here is a very poor, and obvious, Mark McGwire forgery:
Anyone that knows McGwire signatures at all will identify it as the pathetic forgery that it is.
Remember, this is one of Ebay's approved third party authenticators. Gives you a nice warm feeling of confidence, doesn't it?