That is more than likely the purity of the silver, though the most common purity marks are 800, 925, 950, and 999 (meaning 80%, 92.5%, 95%, and 99.9% pure silver) (I wonder if it may be an "800" with any combination of wear/scratches/marks on the zeros that make them appear to be other numbers?).  It could also be a pattern mark, but it's hard to say without a pic.
Re: What does the stamped number 839 mean on silver antique ...
 That is more than likely the purity of the silver, though the most common purity marks are 800, 925, 950, and 999 (meaning 80%, 92.5%, 95%, and 99.9% pure silver) (I wonder if it may be an "800" with any combination of wear/scratches/marks on the zeros that make them appear to be other numbers?).  It could also be a pattern mark, but it's hard to say without a pic.
Re: What does the stamped number 839 mean on silver antique ...
Without any other markings being present I'd say it's just a mold/model number.