Stigma (letter) Stigma (letter) Stigma (ϛ) is a ligature of the Greek letters sigma (Σ) and tau (Τ), which was used in writing Greek between the Middle Ages and the 19th century. It is also used as a numeral symbol for the number 6. In this unrelated function, it is a continuation of the old letter digamma (originally Ϝ, cursive form ), which had served as a numeral since antiquity and was conflated with the σ-τ ligature in the minuscule handwriting of the Middle Ages. The στ ligature (, ) was one of many ligature forms that came into widespread use as
San (letter) an acute accent) or by ⟨σ̱⟩ (sigma with a macron underneath). Note, however, that the same symbol is used to denote the unrelated letter waw () in Pamphylia (the "Pamphylian digamma") and was also the form of beta () used in Melos. The Ionian letter , which later gave rise to the numeral symbol Sampi (ϡ = 900) may also be a continuation of San, although it did not have the same alphabetic position. In the Greek script used for writing the Bactrian language, there existed a letter resembling a ""þ"", which apparently stood for the sound (transliterated as "š")