The form of Latin S arises from Greek Σ by dropping just one out of your 4 strokes of that letter. The (angular) S-condition made up of 3 strokes existed for a variant of your 4-stroke letter Σ by now in the epigraphy of Western Greek alphabets, as well as https://budnaked42085.blogrenanda.com/37381625/not-known-factual-statements-about-bud-naked