According to Warman’s Antique Jewelry, screw back earrings date from 1909 and although still used, they are not common on new pieces.
An exact date is not available for when the stamp STERLING was first used on Native American jewelry.
According to some sources, the STERLING stamp appeared after 1932.
Most Native American made items from the 1930s and before would not have a STERLING stamp nor any artist hallmark for that matter. But there are no hard and fast rules when it comes to hallmarks – there are always exceptions.
Some items made in the 1940s to 1950s might have the STERLING stamp, most notably, those made by Bell Traders during that time period.
But in general, Native American artists began using the STERLING stamp in the 1950s and 1960s. Since then, the STERLING or Sterling or 925 stamps are quite common as are artists’ hallmarks.
.925 or 925 indicate that the item is 92.5% silver which is the requirement for something to be called sterling silver.
In the vast majority of cases, if a piece of Native American jewelry is stamped with one of the above marks, the item is made from Sterling Silver.
If an item is not stamped with one of the above, this does not necessarily mean the item is not made from sterling silver. Most vintage sterling silver Native American items do not have the STERLING mark.
The only definitive way to know is to perform an acid test.
Most Native American jewelry is made from sterling silver which you can read about here.
This particular concha belt made in the 1950s by Kewa silversmith Herb Coriz is made from pure silver ingots.
Thus it is stamped .999 rather than the .925 for Sterling Silver.
However, he made the buckle, which receives the most stress, from sterling silver.