My guess is that there will be no « official » answer to your question, simply because there is nothing on the back. Either « be bold » or look at http://commons.wikimedia.org/wiki/Category:Wikimania_2007_Wikiball
Yeah, this is the backside of the Taiwan-ball: http://commons.wikimedia.org/wiki/Image:MR_Wikimania_1-07.jpg
The project logos are on the northpol and the sponsor-logos on the south. I still think the project logos would be nice. :-P Some other suggestion?
Ting