Windows 8.1 Preview shows evaluation copy on wallpaper

That is normal since it is an evaluation version that will expire on January 15, 2014.

Humm, I'm registered and after registered that info disappeared

also I chose not to install until next month

Update for Windows 8.1 Preview for x64-based Systems (KB2863147)

Download size: 247 KB

You may need to restart your computer for this update to take effect.

Update type: Recommended

Install this update to resolve issues in Windows. For a complete listing of the issues that are included in this update, see the associated Microsoft Knowledge Base article for more information. After you install this item, you may have to restart your computer.

More information:
http://support.microsoft.com/kb/2863147

Help and Support:
http://support.microsoft.com

Check this:

[How To] Remove Watermark (Build Number Info) In Windows 8.1

http://www.kapilarya.com/how-to-remove-watermark-build-number-info-in-windows-8-1

This I strictly illegal with the things( not to do under the Microsoft terms license agreement).

I am very supprised the admins allowed this to be posted. Any reverse of the files of windows and license is illegal.

You must notify Microsoft of the change and wait for approval.

Legal way. If installed with windows 8 go to activate reboot there is a flaw in how the evaluation works and will not report to MS for the upcoming update this also does not allow the water mark to show after manual activation. Do not install the mentioned update I previously mentioned. This update will allow the notification of the windows 8.1 water mark to remain on desktop for the upcoming release of windows 8.1.