What motor vehicles are subject to the no-overtaking rule indicated by this sign?

This traffic sign indicates a no-overtaking zone specifically for certain types of vehicles. The red-bordered sign with a truck and a car means that heavy vehicles (like trucks) are prohibited from overtaking. The additional smaller sign below with "auch" (meaning "also") and the images of a bus and a car with a trailer extends this no-overtaking rule to include those types of vehicles as well.

The key point is that the no-overtaking rule applies to coaches or buses (as shown on the smaller sign), not to all vehicles like single-track motor vehicles (motorcycles) or regular cars without trailers. This is because coaches and buses are large vehicles that can pose safety risks when overtaking on certain road sections.

In summary, the rule restricts overtaking for heavy motor vehicles, including coaches and buses, but not for smaller or lighter vehicles such as cars without trailers or motorcycles. Your selection was correct because the sign explicitly includes coaches or buses under the no-overtaking rule.