Authentic Rolex watches come with certain features that are hard to replicate, such as the flange (the space between the dial and the crystal), which is engraved with the Rolex logo. The serial and model numbers, found on the side of the watch case, should also be clear and neatly engraved. Most importantly, original paperwork and box, if available, help to confirm the authenticity. For peace of mind, you may consider having the watch authenticated by a reputable watchmaker or dealer.