"Water-mark" Natural Recordings by Native Speakers
A watermark is:
1. A translucent image or mark, typically a logo or text, permanently embedded in a document or image, usually faintly visible when viewed at a distance or a reduced size.
2. A stolen or illegally copied copy of a song, film, book, etc., from a internet source leaving a embedded invisible signature that the copyright holder can trace back to the individual who downloaded the content.
3. To apply a subtle translucent layer to cheese or fruit to make it seem fresh, although the term is informal and more of a phrase one might use in casual conversation.