1¢ Washington Head
Perf 10

You must first determine if the stamp was printed using the flat plate or rotary press method. Note that no offset stamps were issued perf 10. If it is rotary press it does not need to be checked for watermark, it is unwatermarked and is Number 543. However, if it is flat plate, you must determine the watermark type.

Printing Method Watermark Size of Frame Number
Flat Plate Single-line 18.5 x 22 mm 424
Booklet (FP) Single-line 18.5 x 22 mm 424d
Flat Plate none 18.5 x 22 mm 462
Booklet (FP) none 18.5 x 22 mm 462a
Rotary "experimental" none at least 22.5 mm high (taller) 543

None of the above stamps are candidates for forgery, they are all quite common.

Washington Franklin Identifier Tool