The shape of Latin S occurs from Greek Σ by dropping just one out from the 4 strokes of that letter. The (angular) S-form made up of a few strokes existed as being a variant from the four-stroke letter Σ already while in the epigraphy of Western Greek alphabets, as https://bud-naked-flower64208.webbuzzfeed.com/31842771/5-easy-facts-about-bud-naked-kits-described