I'm not convinced it's authentic but apparently some people are considering the current bid.
a) The beginning isn't right. I have never seen a Richthofen autograph in which the capital "R" of his last name is
attached to the beginning of his autograph as one continuous scribble. I've always been able to easily identify the "R", but not here. Which scribble is the "R"? It's all connected.
b) Where's the flick of the pen above the "R"?
c) This autograph is s-o-o-o-o incredibly dark. I have not seen such darkness from an 80+ year old autograph. In many cases from postcard signatures this old, the autograph has faded so much it's hard to completely make it out. However in this case, you can spot this autograph from a mile away.
d) It would appear to me that the ink was written
over the silver oxidation around the edges of the aged postcard rather than the ink aging
with the postcard. Take a good close gander at that.
I'm no expert but looks like a fake to me and whoever signed it practiced well before the final "signature".
Caveat emptor!
.