I have an exact set of those that are sterling.
They are stamped on the bottom though.
Do the nitric test.
-a small drop of nitric, let it react, watch the color. Should be clear to faintly blue.
-after reaction completes, wipe it, put another drop in the same spot, if its plated (after 2 or 3 drops in same spot) it will be bright blue/green from the substrate metal.