Illinois "Duo Style" Enamel-Cased Sterling Silver Pendant Watch Art Deco Patented by Louis A. Eppenstein The "Duo Style" marking on enamel-cased pendant watch, along with the inscription "Pat. Mar. 30, 1926," suggests that the watch case design was patented on that date. This patent, numbered USD69576S, was granted to Louis A. Eppenstein and assigned to the Illinois Watch Case Company, a prominent American manufacturer known for producing high-quality watch cases during the early 20th century In Great Working Condition, Keep Very Accurate Time. Just recently was serviced. Please have a look at our vintage watches we have constantly listed on Chrono24.