Someone once told me that the symbol on the 28, and some of the other symbols used over the years on S&Ws, come from late 19th century advertising that the company did.
They're just graphic elements, but they, through use, became S&W graphic elements.
True or not, I don't know, as I'm not familiar enough with S&W's advertising of that time frame, but I do seem to remember seeing that symbol, or one similar to it, on the cover of a very early 20th century catalog.