S NO FURTHER A MYSTERY

The shape of Latin S occurs from Greek Σ by dropping 1 out of your four strokes of that letter. The (angular) S-form made up of 3 strokes existed as a variant on the 4-stroke letter Σ currently during the epigraphy of Western Greek alphabets, plus the a few and 4 strokes variants existed alongside one another while in the classical Etruscan alpha