Well I just went through this stuff a few months ago. I bought a bike off ebay and found out it had a Canadian title.
Which turned out it didn't make and difference since all bikes made for Canada meet US DOT and EPA standards.
Now yours if made for export to Germany didn't have to meet the standards. Thats why you don't have the sticker.
So your best bet is go to Customs and see what your going to have to do to get it exported back to the US.
By what I've found out it sounds like you'd be money ahead to sell it over there and buy one when you get home. It sounds like a realy expensive deal and a lot of work.
Good luck your going to need it.