You need either watermark detection fluid or if your OK with using it (I do) Ronson lighter fluid will work and a black glass or plastic surface to put the stamp on. Put the stamp face down onto the black surface, place a couple of drops of fluid(enough to completely dampen it) onto the stamp. If there is a watermark, it will be a single line watermark (as opposed to a double-line) of one of the letters USPS (or a partial of one of these letters). The fluid makes the letter stand out as a darkened line compared to the rest of the paper.
Do you have access to a Scott U.S. Specialized catalogue? There is a section in front explaining Watermarks. If not, go to
www.1847usa.com and read up on watermarks at that site.
If the stamp is a type II and has a watermark, it would be a #454. If there is no watermark, it would be a #491. #454 is pretty common but the #491 isn't and has a pretty high cat. value. The cancel covers up one important area on the stamp that help determine if it is a type II or type III, but it does appear to be type II as best I can tell. I believe its clearly a rotary press stamp, and if it turns out to be a type III, it would be a #455 or #492 depending upon whether or not its watermarked paper--both fairly common stamps.
Single line watermarks are sometimes hard to see, especially when only a small part of the letter is present on the stamp.
