Stigma (letter) sigma form ς never occurs inside a word and is never used as a numeral either. Uppercase forms of stigma as a numeral (Ϛ) are rare in practice; when they occur, they can often be confused with uppercase forms of another numeral symbol, koppa (Ϟϟ), which stands for 90. Stigma is encoded in Unicode as "Greek letter stigma" U+03DA (Ϛ) and "Greek small letter stigma" U+03DB (ϛ). 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
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")