vintage serengeti sunglasses Tortoise Shell Brown Amber Lens Etched S

These are in great condition. The hinges are still firm. I do not see any visible scratches are markings on the lenses.  They do not have a item number on them. They do, however, have the name of the manufacturer on the back of both earpieces along with an S that is etched on the front right eyeglass lens.  Please examine all photos provided carefully. I am not a collector. I bought some sunglasses at an estate sale and I am researching and finding out as best. I can the information on each pair.  As with an vintage eyeglasses, there could be age related, where although Im not physically seeing any on this pair of glasses. Im not an expert.