The eagle was originally red; it was changed to black on the death of Ruger's partner, Alex Sturm. The earliest automatic pistols are sometimes seen on auction or in collections described as "red eagle" guns.
I note that now Bill Ruger is gone, the company has chosen to eliminate the "S" from the intertwined "SR" in the logo. Even though the company remains Sturm, Ruger & Co., Inc., Sturm's name is gone from most of the company's literature.
Incidentally, the first pistols had no special name. They were simply called "The Ruger Automatic Pistol". When the target version came out it was called the Mark I, and the original pistol then became the "Standard Model".