Years ago when I was in Prepress at Kingsport Press, we did a Cindy Crawford book. I told the art department guy that while he was out I fixed the photos before sending them to make printing plates: I removed that unsightly mole off her lip. (I was pranking him.) He was not amused. That was her trademark beauty mark.
Same deal I guess with my Marlin 39A Mountie and Taurus Model 72 both with takedown screws. It's an unsightly feature that has become a classic beauty mark. I'll admit when I saw my first Marlin 39 the takedown screw looked odd to me. It had a use but it still looked odd.
In my repro of the 1897 Sears Roebuck Catalog, the takedown screw knob is visible (w/o coin slot) on the Marlin Model 1891 leveraction in .32 rimfire/centerfire convertible, and on the Marlin Model 1892 leveraction in .22 short, long, longrifle. The Model 1892 evolved into the Model 1897 which with slight changes became the Model 39.