The shape 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 a few strokes existed as a variant from the 4-stroke letter Σ now in the epigraphy of Western Greek alphabets, as well as https://marcokkdzv.ageeksblog.com/30497375/the-bud-naked-concentrate-diaries