Believe it is a fitters / assembly marking. Parts for Winchesters mass produced and proclaimed interchangeable, still required a certain amount of fit and filing. These marks are left by the men who assured this quality, both mechanically and aesthetically. These markings were extensively used and follow no apparent pattern or sequence. When you see similar numbers but found in a square, diamond or circle, or if underlined, those are left by an inspector. Hope that helps.
Matt
