|Perfs & Orientation||US Number||Watermark||Often faked by altering|
|Perf 8.5 Vertical Coil||391||single-line||344 or 384 (add perfs)|
|Perf 8.5 Horizontal Coil||393||single-line||344 or 384 (add perfs)|
|Perf 12 Vertical Coil||349||double-line||332 (trim) or 344 (add perfs)|
|Perf 12 Horizontal Coil||353||double-line||332 (trim) or 344 (add perfs)|
|Perf 12 Vertical Coil||386||single-line||375 (trim) or 384 (add perfs)|
|Perf 12 Horizontal Coil||388||single-line||375 (trim) or 384 (add perfs)|
Note: a stamp perforated horizontally is known as a "vertical" or "endwise" coil and a stamp perforated vertically is known as a "horizontal" or "sidewise" coil.
Perf 8.5 Coils – There is no need to check the watermark on these stamps for identification purposes, they are all single-line watermarked. It might be a good idea to check for it anyway, since these stamps are sometimes faked by perforating the unwatermarked imperforate stamp. See the caution below.
Perf 12 Coils – These stamps must be checked for watermark.
Perf 8.5 Coils – If the stamp has a double-line watermark it is clearly a fake made from the US344 and should fool no one. The fakes made from the US384 may prove a little more difficult. In any case, one should also examine the perforations. If the perforations appear genuine, there is a very good case that the stamp is genuine since there is no corresponding perforated 8.5 stamp from which to make the fake. Also, pay particular attention to guide line pairs, which command a high premium and are very often faked by simply drawing in the guide line with a similarly carmine-hued ink.
Perf 12 Coils – US349, US353, US386 and US388 are often faked. All of these stamps are prime candidates for fakery, and all but the single-line watermarked horizontal coil are in that gray area in which the cost of certification can often be more than the cost of the stamp. The US388 is considered to be one of the most commonly faked stamps in U.S. philately, somewhat surprising since it is folly to buy this stamp without certification.
Particularly suspect are well-centered stamps. Although many fakes are made by trimming a fully perforated or perhaps a large margined straight-edge copy of the two cent sheet stamp, the fakes are easily recognized since they often measure less than the proper width of 21.5 mm in the case of the vertical coils and the proper height of 25 mm for horizontal coils. The measurement is made from edge to edge on the non-perforated sides.
The more dangerous fakes are made from the imperforate stamp. The perforations must be examined closely to guarantee authenticity. Keep in mind that much of the stock of the imperforate stamps have been given fake perforations to resemble their more expensive coil counterparts.