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.
|Watermark||US||Privately Perforated by:|
|Double-line||344||Attleboro; Brinkerhoff I, II, IIa, IIb; International Vending Machine; Mailometer I, II, III, IV Schermack I, II, III; USAV I, II, III|
|Single-line||384||Brinkerhoff II, IIa, IIb; Farwell 1, 2A3, 2B3, 3A2, 3B4, 4A3, 4B3, 4A, 4B, 4A5 Mailometer I, II, IV; Schermack II, III; USAV I, II, III|