I haven't seen the postcard before but the writing on the left and Brando's autograph are printed.
You can tell because the writing on the left in blue is the same color as the blue printing on the postcard. Plus compare the smoothness and flow of the ballpoint pen address on the right.
It reads like a commercial to to guys and dolls. He would have been a native german speaker to write this postcard as it basically is in perfect german grammar.
"Damon Runyon is one of the big storytellers of the present he is able to create a big city millieu. Immortal his guys and dolls. That is why our movie with the same title is worth making and seeing"
Funny that if this is printed that they even misspelled on word.