Suspect Scott #348, Used Single.
This is a moderately priced stamp with a catalogue value of $37.50. This coil is often faked and can be manufactured from the following stock: adding fake perforations to a trimmed imperforate #343, adding fake perforations to the imperforate vertical coil #343V, trimming the perforations off the left and/or right of a perforated #331 and trimming the perforations from the left or right of the #331a booklet stamps.
The watermark is double line “P” in the upper left corner that is inverted, reversed and reads horizontal which eliminate the possibility of the suspect being a booklet single which would have a watermark that reads vertical.
The left edge is a natural straight edge showing the guide line. The Philatelic Foundation has certified a number of stamps as genuine showing a guide line on either the left or right edge. The right edge on the other hand shows obvious perforation remains at the top.
Conclusion: In my opinion the suspect is a #331 perforations trimmed from the right hand side.
Reference material used:
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