Stigma is a ligature of the Greek letters Sigma and Tau. It has a numeric value of 6 like Digamma. The Greek letter ς (called Stigma) is used for the number 6.,,,, It’s my guess that the Greek letter ς and the English equivalent S are so derived from the resemblance to the erect hissing cobra (the invert image of the Uraeus photo on the left). This also explains why the words snake, serpent and Satan (= “hisss”) all begin with an S symbolizing the flames (i.e., also a “hisss”) of destruction. The 3 letters SSS (in Greek Σ Σ Σ) were the symbol of Isis, which is thus connected with 666. http://www.cropcirclesdeciphered.com/decipherkeygematria.htm