Microsoft has released KB2902864 update to remove “Windows 8.1 SecureBoot isn’t configured correctly” watermark from the desktop wallpaper in Windows 8.1 and Windows Server 2012 R2. Affected users can download and install the update. After applying the update, you need to restart your computer for changes to take effect.
FYI, after upgrading or installing recently released Windows 8.1, some users got “SecureBoot isn’t configured correctly” watermark on their desktop. Microsoft has addressed that issue with this update.
Till this update, to get rid of this watermark Microsoft suggested users to turn on or setup Secure Boot correctly, now you no longer need to play with your BIOS settings, just install this KB2902864 update and watermark will disappear after the restart.