What is digam?

Digam is a Unicode character that resembles the lowercase Greek letter "stigma" (ςτ), but with its vertical stroke extended downwards, and with a horizontal line intersecting the stroke at the bottom. It represents the combination of two sigma (ΣΣ) sounds in the Greek language and was used from ancient times until the modern Greek alphabet was adopted in 1982. The name "digam" is derived from the Latin term "disigma", meaning "double sigma". The Unicode encoding for digam is U+03DC (Ϝ) for the uppercase version and U+03DD (ϝ) for the lowercase version. The character is rarely used outside of academic and historical contexts.