What does a js stand for on a siver dime?

The "JS" on a silver dime stands for "John S. McCoy," the designer's initials. McCoy was responsible for the design of the reverse side of the Mercury dime, which was minted from 1916 to 1945. The Mercury dime features a depiction of Liberty wearing a winged cap, and the "JS" is a subtle nod to the artist's contribution to this iconic coin.