Sorry I didn't reply to this one sooner. Identifying an autograph is a very precise art, and even more so with Beatles memorabilia, with it being such a popular field. There are millions of ways to identify if a signature is real and in this day and age it is very difficult to get away with a fake. Like art forgeries, proper authenticators (any item you buy that is of any worth should hae some guarantee of authenticity) will employ laser technology and use examples countless examples of the signatures as reference. Given the speed at which the signatures are done and the hand movement required, you would be lucky to get away with it.
Auction houses that are respectable will always provide a cerificate of authenticity, which has usually been approved by an expert in the field.