I don't know how to post the great link that Bag Fetish did, but, I looked in the FAQ section and found this:
"Authenticating a Coach product
Please visit our Authenticate This! thread at the top of the Coach Shopping sub-Forum for specific questions (posting multiple pictures helps a lot, as well as posting eBay auctions, etc).
In general, signature pieces are easiest to determine authenticity, signature bags are always symmetrical and a mirror image of the other side. This is usually easy to spot, counterfeiters usually don't get this right.
Also, signature bags do not also have signature linings. And in all bags, there is a creed with a stamped serial number. No creed in a bag = FAKE."
Hope this helps.