What do such traffic signs indicate?

The sign shown indicates the number of an autobahn (German motorway). In Germany, autobahn route numbers are displayed on blue signs with white numerals. This helps drivers identify the specific motorway they are on or approaching.

Such signs do not indicate distances or European road numbers. European roads use a different sign format, usually white letters on a green background with the prefix "E."

Knowing this helps you navigate the motorway network accurately and find your route more easily. Always look for these blue signs when driving on the autobahn to confirm your route.