Watermark Check
This stamp must be checked for watermark. Note that these stamps are seldom faked, rather they are the starting point for many of the more dangerous forgeries in U.S. philately. The primary reason the imperforate stamps were issued was to supply stamps to the vending machine manufacturers who in turn applied their own perforations in order that the stamps would feed properly in their machines. Imperforate stamps were also supplied to collectors upon request and these are the stock from which many of the flat plate coil fakes were made.