Eagle icons
It's an Eagle, its a Phoenix, its a Dragon, its on some of Hank Williams Jr.'s albums (with permission!). Neither Sturm, nor Ruger are around to ask, anymore, and unless you have something in print, from them, stating Sturm's inspiration, its all just guesses.
Eagles have been used throughout history, throughout the world as symbols. If Eagles lived there (or had lived there) somebody used some variant of a stylized Eagle in their standard, logo, coat of arms, on their flag, etc.
Several of the ruling houses of Europe used eagles as their sign. Many different governments have also. The US does, the ROMANS did! Its not just a Nordic thing. (ok the Germans use it a LOT
)
Personally, I think the reason that the nobility and governments use(d) the Eagle is because a vulture was too close to the truth.