That's not a watermark, that's an Overlay ... somehow, the Wrench Icon for settings for your program monitor got clicked to turn on overlays. Go to the wrench icon in the program manager, and in the long list that pops up, near the bottom, uncheck Overlays.
The rest of the issue is a video card driver/OS mismatch issue. To check, in Project settings dialog, set Mercury Acceleration to "software only" and if you screen looks proper then you've got a video driver issue.
At that point, go to the manufacturer's site for you GPU card, and check manually that you have the latest driver for your GPU. If not, update. If you do, you might try rolling back a driver version.