I went to the Smithsonian museum and I saw this displayed, it says the swastika on the inside of the nose of the Spirit of St. Louis was a native American good luck symbol. This article says it could be but none of the swastikas are straight like the one in on the piece.
This article seems to indicate that the swastikas used at this time in history were based off of the Sanskrit symbol. I'm wondering if the person who wrote the description saw "Indian" and thought "Native American" when what was meant was from India.
The Swastika was a common motif from the American Southwest. It was also known from Sanskrit and from Europe. The source of its adoption in the early twentieth century would depend on testimony at the time since after-the-fact interpretations are suspect in view of how the symbol became loaded with baggage from its Nazi appropriation.
I question the Smithsonian display since the symbol in this context may have been from Europe or it may have been from India or North America, but anything stated after the mid 1930s would have been affected by the emerging politics of Hitler. Was the Smithsonian display based on primary source material from the 1920s or is it a later effort to turn aside assertions that it was based on fascism? that would be the question. Given Lindberg's later flirtation with Hitler, this is a particularly sensitive issue, even though in the 1920s, the appearance of the swastika in this context would have been completely innocent and innocuous.