Hi Jürgen,
The simplest way I look at is to by having an image or sort as a watermark in master page.
Of course you need to remove the watermark before you transport it to next environment.
Isn't this you are after ?
If you are after something generic (like with out chaning the form) I think there are ways to tweak it around, let me know is this you are after.
Cheers,
Sai