The Umwelt-Plakette or Feinstaubplakette is a sticker you put on your car’s windscreen. It proves that your car meets low-emission standards. It allows you to drive in low-emission zones.
You get that sticker when you register your vehicle. You can also buy it from garages and gas stations.
Motorcycles don’t need an Umwelt-Plakette; they are always allowed inside environmental zones.