A picture of the mark would help me to be sure, but I have seen a Maltese cross hallmark on a ring by Ostby & Barton Company, started in 1879, incorporated 1893. Ostby was one who lost his life on the Titanic, his daughter however did survive. I think the business continued until 1950. They usually sign their jewelry OB with other marks possible, one being a maltese cross. I do not know if a maltese cross alone was ever used by the company.
