What does this traffic sign indicate?

Your answer is correct. This sign indicates the end of the autobahn (motorway) in Germany. When you see this sign, it means you are leaving the controlled-access highway and normal road rules apply again.

On the autobahn, certain rules are specific, like no general speed limit unless posted otherwise. After this sign, these special autobahn rules no longer apply, and you must follow the standard traffic regulations for regular roads, including any speed limits or restrictions.

So, whenever you see this sign, be prepared for possible changes such as reduced speed limits, intersections, traffic lights, and other traffic controls typical for non-autobahn roads.