Which vehicles are not allowed to use a road sign-posted like this?

The sign displayed indicates a prohibition for bicycles. According to German traffic regulations, this means that bicyclists are not allowed to use the road where this sign is posted.

In general, the restriction may also apply to other vehicles depending on the specific context or additional signage present in the area. In this case, if the correct answer identified a combination that included bicycles, it was correct because bicycles are explicitly banned. Understanding this helps ensure safe use of roads and promotes orderly traffic flow, especially in areas where bicycles could pose a risk to their riders or others.

Always pay attention to road signs, as they provide crucial information about the allowed and prohibited vehicles in particular areas.