What do such traffic signs indicate?

The sign depicted indicates the number of an autobahn in Germany. Specifically, it designates the autobahn as A48. Autobahn numbers are typically displayed on blue signs with a white number, which helps drivers identify the routes they are traveling on.

In the context of your question, selecting this as the only option is correct because it specifically identifies a roadway type within the German traffic system. Other options, such as distances to petrol stations or European road numbers, are not applicable in this case. Understanding these signs is crucial for navigation and road safety in Germany.