Officially, the name of the sign is “Prohibition of overtaking single-track vehicles for multi-track motor vehicles and motorcycles with sidecars”.
Specifically, this means that from traffic sign 277.1 onwards, all single-track vehicles such as bicycles, mopeds or motorcycles may not be overtaken by multi-track vehicles – i.e. cars or trucks – and motorcycles with sidecars.
This overtaking ban is fundamentally based on Section 5 Paragraph 4 of the Road Traffic Act and is intended to protect single-track vehicles from the risk of local conditions when overtaking. This can be the case, for example, with bottlenecks, downhill and uphill stretches or generally confusing traffic situations.
Disregarding the traffic sign can be punished with a fine of 70 euros and a point in Flensburg. You can find out more about what the round, black and white traffic sign on the Autobahn is all about here.