The only sure way of telling a Rolex watch is genuine is to take it to an authorized Rolex watch retailer. They are trained to recognize even the best fakes.
If you are in doubt about the authentisity why not either consult a copy of the "Rolex Report", an authorative book on all Rolex models, or take it to a certified dealer who will be able to tell you if it is a fake or not.
A new genuine Rolex comes always with international guarantee card. If you are buying a 2ndhand one, make sure you can trust the person, as there are lot of imitates
