Just in case anyone wonders: there is no watermark in the headset, just a logo on the monitor mirror that serves as injection indicator. I changed the thread title for clarity.
That said, there is an ini option that should do the trick. Go to C:\ProgramData\Animation Labs\vorpX and open vorpX.ini with a text editor. In the [GUI] section set bShowWatermark to False.
The C:\ProgramData folder is hidden per default by Windows. If you can’t see it, enable ‘Show hidden files’ in the Explorer options.