A couple of thoughts on this. The bracelet is hand made. The bracelet shank is fashioned from three strips of milled sheet (milled sterling sheet from a supply house, rather than coin silver). The sheet itself was cut with a hand shears into three equal strips, with the two outside strips being shaped with pliers, and then soldered together with the straight center strip to form the shank. The stamps are handmade in the Navajo fashion, and as others have pointed out, the swirls are impression tool marks from stamping on the back side of the plate.
The stone looks like Persian turquoise and is natural, but is a lower grade stone. I would estimate the bracelet was likely made in the late 60s or early 70s rather than in the 40s or 50s, and is made in the old fashioned Fred Harvey style. However, the half round sections embellishing the top and bottom of the setting look to me more like early 70s work, than anything from the 40s or 50s. Probably around fifty years old, give or take.