Mystery sterling mark, cartouche-like shape, no letters

[aaadams]

I have a tea set, teapot, coffeepot, creamer, sugar and wasterbowl. All pieces are marked STERLING with the symbol and the pattern number 223.
I have searched through several marks websites and have come up dry. Would appreciate if anyone can identify this hallmark. My guess is this set is 20th century. Many thanks.

[cannon50]

New member here. I just wanted to say that I found what seems to be the same piece listed as Durham and with the same number at replacements.