These sterling silver "fingernail" thimbles were made by the late jewelry-artist, Carrie Adell (14 Nov 1931-15 July 2001). These particular ones are not my favorites of her thimbles, but it was the only photo I could find, so here it is, tarnish and everything. On my favorite of her thimbles, the fingernail part has a design that looks sort of like sand thats had water wash little ridges through it. Ms. Adell became renowned for her beautiful multi-precious-metal jewelry and small handmade beads she called "Touchstones." She had (at least) two registered U.S. Patents (that I could find) : 5515584 and 6108878, both for wire connection systems used in jewelry. Her hallmark is shown below at right. Her thimbles that I've seen are usually hand-signed, either C. Adell or Carrie Adell.
More information about her life and work can be found at the Patina Gallery (Santa Fe, NM) website and at her daughter, Jo Adell's website, knot-working.com. Jo is also an accomplished jewelry-artist.