Found in August 2004 on my sister's mail, this cancellation with an inverted picture.
The stamp itself was issued 6 May 2004 for the 1250 years of saint Boniface. He is considered the patron saint of Germany. That explain the combination of the christian cross and the colors of the German flag.
The inverted panda is, when the head's up, is the WWF's logotype, the non-governmental organisation defending the nature.
In case of quick intels about German stamps issued since 2000, see the Briefmarken-Archiv (in German). The philatélic site of the Deutsche Post has got more informations about the stamp and its illustration, but you can only find the stamps always sold.