Berlin, Hannover and Cologne have banned environmental-unfriendly cars from their city centers. All cars entering inner city zones have to display a sticker (green, yellow or red) depending upon the amount of pollutants emitted by the vehicle. In the most restrictive zones, only green-stickered cars will be allowed to enter. For more details on which vehicles are affected (largely old diesel vehicles), click here (PDF). Note that you need to have these stickers in certain German cities otherwise you will be fined. You can buy the stickers from Umwelt-Plakette.de.
I am very pleased to see these cities taking concrete steps to clean up the air. I am hoping that Amsterdam does the same. But what happens if you are a tourist? How are you supposed to get those lovely little stickers?