First of all, on a New Model Navy, the barrel top flat is stamped: "PATENTED DEC. 17, 1861. MANUFACTURED BY REMINGTON'S, ILION, N.Y."
A New Model Army will have: "PATENTED SEPT. 14, 1858, E. REMINGTON & SONS, ILION, N.Y., U.S.A. NEW MODEL"
A Beals will have the markings: "BEALS PATENT, SEPT. 14, 1858. MANUFACTURED BY REMINGTON, ILION, N.Y."
If there are no barrel markings, it has been filed off and refinished, and may or may not be original. There should be no reference to "Black Powder Only" or such markings, as the originals didn't need such a warning. There should be no proof marks as seen on Italian guns, and the serial number should appear on the bottom barrel flat and the side of the grip frame, under the wood. Nowhere else.