Question about the Great Gatsby that has always bugged me (obscure detail, short question)?

That little detail has always played up in the back of my mind whenever I think about The Great Gatsby. Yes, the swastika was a Hindu symbol of luck going back some thousands of years, but it's still weird to see it in connection with an ostensibly Jewish character so many years before World War II, kind of like it's prophetic. In response to another answer here, I wonder if Fitzgerald ever got hold of a copy of Mein Kampf; it seems doubtful though, since the first English editions weren't published till the late 1930s and '40s (and Fitzgerald died in 1940).