If you made the purchase at an authorized store, then it is not likely to be a fake, but every brand will come with a different type of warranty card. In some cases, for example, there will be a seal on the price tag with a bar code and serial number. At the time of purchase, the store will transfer that seal to the warranty card, thereby validating the warranty. If you don’t have the serial number, go back to the store where you bought the watch and ask them about it.