watermark

noun

1. a line marking the level reached by a body of water

   noun.location

   Synonyms water line

   Source: WordNet 3.0

2. a distinguishing mark impressed on paper during manufacture; visible when paper is held up to the light

   noun.communication

   Source: WordNet 3.0

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

   noun

   Source: webster1913