Coil Type - There is no need to check watermark or printing method, other than for authentication purposes, these stamps must both be flat plate and double-line watermarked. 

Caution:

Both of these stamps can be easily faked by perforating Scott 347 stock, although Scott 347 is not all that cheap and the forger does not stand that much to gain by doing so. The more common fakes are made by trimming the sides off used Scott 335 stamps, since the used 335 is quite common. We would highly recommend purchasing used copies of either stamp with certification or from a reputable seller only.

Washington Franklin Identifier - Home Page