Sigma was a letter in the Tionese alphabet. Sigma was often used as a call sign for Imperial starships, often transports such as the Delta-class DX-9 stormtrooper transport. Transport Sigma 1 and Sigma Squadron of TIE Phantoms are such examples.
- Star Wars: X-wing (First appearance)
- Star Wars: Rebel Assault II: The Hidden Empire
- Star Wars: TIE Fighter
- Star Wars: X-wing vs. TIE Fighter
- Star Wars: X-wing Alliance