I haven't tried to scan the watermark because the scanning light from the scanner is so bright, that I thought it wouldn't turn out. If you use a flatbed type scanner (with a lid) you can try leaving the lid open and placing a light source of sufficient intensity above the scanner and note. This might provide an image you could live with. I just got to work, but I might try this tonight and see for myself, too.
Dunring the darker, winter months, I have (Slowly) been taking photos of the watermarks on my banknotes. I have found it is pretty easy for me to use a backlight and then photo them. If you haven't a lightbox or something else to use as a backlight, perhaps you can try to place them on a window in the daylight (taped up in a protective sleeve perhaps) and then photo them.
Good luck.
P.S. That example's watermark is pretty neat!
link to some photos of watermarks