No. Hitler's signature - see this representative example - might look like an S, but it is a stylized A_f in the older German cursive script. The signature is a little sloppy as was the rest of his handwriting. Hitler stopped writing out his full name Adolf for the A_f as he rose to political prominence. It is possible there was an aesthetic reason for how he spelled and styled his first name, but he would hardly be the first political leader to adapt a shortened, stylized autograph, as seen in this more cheerful example.