What kind of wall is this??

Yeah, what kind of wall is this??

when i use as wall, look normal, but, when i'm going to shutdown the computer, appear a watermark (invisible in normal mode)

If I'm not mistaken that's what it does everytime on every Windows computer when you have the shutdown window open.

If I'm not mistaken that's what it does everytime on every Windows computer when you have the shutdown window open.

and.. how we can do a wall like that?