watermark

n. mark indicating the height to which water has risen; design that is impressed in paper and is only visible when held up to the light

v. make a watermark (on paper); impress a design in paper which is only visible when held up to the light

A watermark is a recognizable image or pattern in paper that appears lighter when viewed by transmitted light (or darker when viewed by reflected light, atop a dark background). A watermark is made by impressing a water-coated metal stamp or dandy roll onto the paper during manufacturing. Watermarks were first introduced in Bologna, Italy in 1282; they have been used by papermakers to identify their product, and also on postage stamps, currency, and other government documents to discourage counterfeiting.
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(n.)
See Water line, 2.
  

(n.)
A mark indicating the height to which water has risen, or at which it has stood; the usual limit of high or low water.
  

(n.)
A letter, device, or the like, wrought into paper during the process of manufacture.
  

Noun
1. a line marking the level reached by a body of water
(synonym) water line
(hypernym) line
(hyponym) high-water mark
2. a distinguishing mark impressed on paper during manufacture; visible when paper is held up to the light
(hypernym) marker, marking, mark