Cars without Diesel Particullate Filters (DPF) will be banned from entering German cities starting January 1, 2008.

It will be part of a system in which people will be required to have an inspection sticker on their windshield that signifies they have a DPF filter if it's an old diesel car, AutoBlog Green has reported. Those cars found in city centers without the sticker will be fined 40 euros and one point on their driver's license.
The local German authorities are offering a retrofit option for older cars, but it'll cost owners about 320 euros. Ford is also selling a DPF retrofit kit in Germany.
The move is not so unusual. New Delhi, India, banned dirty diesel vehicles a few years ago.