Watermark

Watermark is a common name for a label in the bottom-right corner of the Windows desktop identifying the operating system version, which overlays the desktop wallpaper. It is most commonly seen in pre-release versions with a timebomb, where it is enabled by default with no option to disable it without tampering with system files, however, it is also possible to enable it on release builds with a registry entry. A distinctive form of watermark is also visible when a Windows system boots in safe mode, which overrides any other forms of watermark, if any.

Watermarks have originally been used by debug builds only. However, during the development of Windows 98 and Windows 2000 they have become widely used to mark pre-release builds regardless of the build type.

History
The first known Windows build known to display some kind of watermark is Windows 3.0 Debug Release 1.14, which displays  in the bottom right corner of its desktop.