I don't think that every decorative element on the old rifles has to have some sort of meaning. For example, the acanthus leaf is a standard baroque decoration that was used in many artifacts and media besides guns back in the 17th century, and originally appears well over a thousand years earlier on the tops of Corinthian columns. It could be, too, that some elements originally did have a meaning of some sort, but were carried on through the years just because it was traditional. Genuine Masonic symbols surely had meaning, but even they may have gone on to live a life of their own because they "looked cool," or however they would have said it then. Meanings could have been attributed to designs, speculatively and after the fact, that were either different in the original concept, or which were put there originally for purely artistic reasons. These days, maybe the most we can say is that it's all about what it means to you, personally, when you add a symbolic element to the design of your rifle.
