Watermark Check: You must first determine if the imperforate stamp was printed using the flat plate or offset method the 1¢ rotary press imperforate stamp was not issued. If the stamp is offset, it does not have a watermark. If it is flat plate, you must check for the presence of a watermark.
|Printing Method||Watermark||Number||Privately Perforated by the Following Companies/Types|
|Flat Plate||Single-line||408||Brinkerhoff I, II, IIa, IIb; Farwell 4A, 4B, 4A5, 5A4; International Vending Machine; Mailometer I, IV; Schermack III; USAV I, II, III|
|Flat Plate||none||481||Schermack III only|
|Offset||none||531||Schermack III only|