The United States Glass Co. used an interlacing U and S for some of their wares. You can see a picture of this mark at the following website:
https://www.great-glass.co.uk/glass%20notes/markt-z.htm#U
Please take a look and see if that resembles the mark you have. If not, you can contact our curatorial department through their online form (https://www.cmog.org/glass-questions). The Corning Museum of Glass does not provide appraisals, as a matter of policy.
If you'd like more information about the United States Glass Co., please let me know.
