U6 Old Berkshire Mills 1881 Watermark On Postal Stationary

Does anyone know where I can see this watermark? I have several U6 Envelopes that have some sort of watermark, but I don't know what I am looking for. They are all half slit open at the top and I don't want to open them up. I can clearly see a watermark, but I don't know what I am seeing.
I've searched on the internet with no luck!

Thanks!


*** Moved by Staff to a more appropriate forum. ***

A U6 envelope should have a watermark that looks like this:



Though there were several variations in how the text (POD US) was situated on the dandy roll.

Hold the open side of the envelope open and toward a light source. The envelope should be positioned between the light source and the viewer's eyes. This technique works best. Results using a light box can be confusing if watermarks on the front and back of the envelope overlap. Another technique is use an LED flashlight inserted into the envelope. A pictorial listing of the watermarks should be handy to aid in identification. Dandy rolls wore with use and sometimes lost bits and pieces.