What motor vehicles may enter an environment zone that has this sign?

Your answer is correct.

In Germany, an "Umweltzone" (environmental zone) restricts entry to motor vehicles based on their emissions to reduce pollution. Only motor vehicles with a green particulate emissions sticker are allowed to enter these zones. This sticker certifies that the vehicle meets strict emissions standards.

Motorcycles are generally exempt from this restriction and may enter without the emissions sticker.

Vehicles that meet the requirements but do not display the sticker are not allowed to enter; the sticker itself is mandatory for access.

Understanding this helps ensure you avoid fines and contribute to reducing urban air pollution.