Check the notification center for information about the issue that causes its appearance. Media Center installation warns about the start-up services Media Center needs and offers to disable them. Once that issue is resolved, your watermark should disappear.
McKay, on 18 January 2013 - 22:57, said:
Yeah, it's always been activated since I first got it.
Sometimes the installation of Media Center will deactivate Windows, have you checked since this issue? If this is the case, just reactivate.