I found the following tip on: http://www.rs-sportscollectibles.com/auti1.html It is important that you are familiar with the basic steps in evaluating a signature. Looking at known authentic exemplars (The word exemplar is from the 15th century Latin word exemplum which means: “one that serves as a model or sample; a typical or standard specimen”. ) of the autograph in question will allow you to make a better assessment and avoid purchasing a possible forgery. A person’s signature, like their fingerprint, is a unique and accurate way of identification. Signatures have distinct characteristics and, when examined by qualified, highly trained professionals can be authenticated with a very high degree of certainty. If you are unsure of an autograph's authenticity, you should seek the opinions of qualified, trained and experienced Forensic Document Examiners (handwriting experts). These examiners apply the science which has been developed over the years to render the best opinion possible.

The best way to be sure, is to hand them the pen and a piece of paper and have a camera. There's a site on the Internet (which I can't find at the moment, sorry) that is one guy's private celebrity's autograph collection. He finds out where celebrities are going to be and not only gets the autograph, but he takes a photo of the celebrity writing the autograph. The thing would be to compare autographs. eBay would be another place to at least see what celebrity’s autograph looks like. I have an autographed photo of Arnold Schwarzenegger and it comes with a Certificate of Authenticity. It looks genuine when compared to other autographs. My all time favorite autograph is of the late James Doohan. (Scotty from Star Trek) I have a photo of me and my brother standing with Scotty. Some celebrity’s take autograph's very seriously and spend hours signing 10 X 8's. As in the other answers, there are plenty of fakes, photocopies and printed autographs. Buyer beware and if you want 100% sure, track down your celebrity and politely ask them for an autograph. Most will be happy to sign. Have more than one pen or marker, a photo (if you want a signed photo), and a clipboard or something hard to write on. Don't have some small peice of paper the size of a drink coaster! Asking for personalized autograph's is pushing it, but if they are not too busy, or if there are not too many other people in line, you should be okay. Scotty would only sign is name, no "to John.” It took me about three years, but I found a child star called Huckleberry Fox (Terms of Endearment) At first we emailed, then I wrote a letter to him. Then I wrote again with a number of publicity photographs. He signed them and mailed them back. Have faith and don't give up.