The hallmarks look like a fancy F enclosed in a lozenge and 800 enclosed in a rectangle. I really do not know. They have traveled a long way during their lifetime and show some signs of wear. I would say there is some soft surface scratch marks as appear on most silver from polishing and use.
You do not feel but see. Just not like brand new silver. There are several cups where the base is dented.
They all sit flat however. Perhaps you can determine the mystery origin of these delightful cups and saucers and let us know. If you would like more images, I will be happy to send them. The item "ANTIQUE SILVER DEMITASSE CUP AND SAUCER SET OF 6" is in sale since Tuesday, April 9, 2019. This item is in the category "Antiques\Decorative Arts\Ceramics & Porcelain\Cups & Saucers".The seller is "torczyne-01" and is located in Saratoga, California. This item can be shipped to United States.