Is there a way to display a watermark on the screen at all times?
Solution 1:
You could try Rainmeter. Customize an existing skin (there are plenty of skins on internet) that includes all the information that you want to show on desktop. Like this:
And you can set it as Position: Stay topmost. It means that it will be always on top even over user windows.
You need to make sure that the user can't kill the rainmeter process.