What cars that are driven within designated environmental zones must display a particulate matter sticker?

In German “environmental zones” (Umweltzonen), a vehicle is generally only allowed to enter if it is marked with an emissions sticker (Feinstaubplakette). This is why all three answers are correct: the rule is based on the vehicle being used in the environmental zone, not on the engine type.

Petrol cars and diesel cars need the sticker because they produce exhaust emissions and are classified into emissions groups. But even cars with electric motors also need a sticker in practice, because enforcement works via the visible sticker on the windshield. Electric cars usually qualify for the best category and can get the corresponding sticker, but they still must display it when driving in an environmental zone unless a local exception applies.

Rule of thumb for similar questions: If you see “environmental zone,” think “sticker requirement for any car that wants to enter,” and then separately check which sticker color (emissions class) is permitted on that specific sign.