What do such traffic signs indicate?

This sign indicates the number of an autobahn (highway) in Germany. Autobahn numbers are always shown on a blue background with white numbers, helping drivers identify the specific highway they are on or approaching. This is important for navigation, as autobahns are major roads designed for fast and efficient travel.

It is not related to distances to petrol stations or European road numbers, which have different sign designs and colors. Recognizing these signs helps you stay oriented on the highway network and follow route numbers for your journey.