So far the St. Andrews cross is the marker for European paths in Germany. However it is not uniformly applied.
Recently the European Ramblers associations have agreed on the following marker. It is to be used in addition to local markers.
This path is to start in Finland and end in Greece. Longer stretches in Finland as well as on the Balkans are either not yet existing or not marked. The total planned length is 8.000 km. Appr. 1.700 km are within Germany from the Danish border to near were the German / Czech / Austrian borders meet. A good short first overview can be found on the website of the European Ramblers Association.
Starting at Krusa in Denmark until Güster in Schleswig-Holstein the E6 runs together with the E1.
So far I have covered the sections from Flensburg until Alt Garge. From Flensburg until Ratzeburg it can be covered hiking from one youth hostel to the next one.