Hi, I can maybe help you a little. According to Lehner’s Encyclopedia of Pottery & Porcelain the mark of O.P.Co. was used from 1885 to the early 1900’s. They made it their priority to make sure all dinnerware etc. was marked with the month, year and initials. by using code numbers so that customers could tell when it was made. If you can’t read it well then I don’t know. They sold a lot of dinnerware to hotels, passenger railroad cars and a lot of this dinnerware was monogramed with the hotel or railroad name or initials. Hope this info helped you some.