Wacht am Rhein, Wacht an der Donau. This can be read in a small verse in the text of the German edition of the correspondence card attached to the post. According to the inscription, the soldiers of the Monarchy and Germany marched to the front with these slogans. As said, these inscriptions could be read on trains going to the front.
Wacht am Rhein (Rhine Guard) is taken from a popular German military song. The term Wacht an der Donau (Danube guard) appeared only during the war, perhaps as late as 1915. During the mobilization of 1914, the slogan “Wait, wait, dog Serbia!” password was used. Little Serbia taught the overbearing Austrian military leadership how to behave, so from the beginning of 1915 the main task on the Balkan front was the defense of the Danube border.
The Kappenabzeichen is also about this changed situation. The Austro-Hungarian buck guarding the banks of the Danube is not preparing to attack, but rather just watching. At the end of 1915, a new offensive was launched with German help, which quickly crushed the remaining Serbian forces. But until then, the Danube sentinel remained in place.