My sincere thanks to axbuhr for referring me to this site () and to the very helpful and knowledgeable Tobias Schroedel (schroedel@sichere.it), an IT-specialist and expert in historical cryptanalysis, who quickly managed to solve the 100 years-old cypher on the card. My sincere thanks also to Philaforum and its administrators for running this wonderful site and for allowing me to post the question.
The encyphered postcard will appear shortly next to the other encrypted postcards that Tobias lists on his website and will also appear as one of the 'challenges' of the fascinating Cryptography website Mystery Twister C3 (), an international Crypto Cipher Contest.
Since I do not wish to spoil the fun of all those who will also attempt to solve the riddle, I cannot, unfortunately, say more. I suggest those very eager to find out what the postcard said or how the riddle was solved to contact Tobias directly (after having sworn to never ever reveal the secret!).