Often overlooked is the reason for this photo (and a series of other, less formal, snapshots in headdress): Coolidge signed into law the Indian Citizenship Act of 1924, granting citizenship to all Native Americans born in the United States. Yes, prior to this date, the country's original inhabitants were not automatically regarded as U.S. citizens. About 2/3 of Native Americans had gained citizenship through a variety of means, some of which required leaving behind traditional cultural practices (see this Oklahoma State site for more extensive information). For making Native citizenship universal, in theory if not always in reality (see this Politico article for information on how some states continued to fight universal Native citizenship), the Sioux made Coolidge an honorary tribal member.
On a truly lighter note, Coolidge and his wife, Grace, were avid pet lovers, caring for dogs, cats, birds, and more exotic species throughout their lives. Here's Silent Cal with his white collies, Rob Roy and Prudence Prim, on vacation in New York:
Here's Grace Coolidge with the couple's raccoon, Rebecca:
Other companions included Enoch the goose, lion cubs named Tax Reduction and Budget Bureau, Ebenezer the donkey and a host of domestic cats. For a complete list, as well as credits for both pet photos above, see the Web site of the Presidential Pet Museum.