Synchronisation is the hard part. I suppose there are a few different ways to do it. One way would be to use a hardware that holds a private key in a secure chip, and whoever has access to the physical watch can sign a message with that key to point to an arbitrary address. This can then be submitted to the blockchain. Confirmation is easy, as the blockchain takes care of that. It would be emitted by a verifiable/trusted public key. If the address is not Rolex's address, the item is fake.