It's sort of a stage name. It's a name she chose for herself.
Susan Alexandra Weaver was born in New York City on October 8, 1949,[4][5] the daughter of English actress Elizabeth Inglis (1913–2007)[6] and American television executive Pat Weaver (1908–2002).[7] Her father served as president of NBC from 1953 to 1955, during which time he created The Today Show.[8] Pat's brother, Doodles Weaver, was a comedian and contributor to Mad.[9] She is of Dutch, English, Scots-Irish, and Scottish descent through her father.[10][11]
At the age of 14, Weaver began using the name "Sigourney" after she took it from a minor character in The Great Gatsby.
it's crazy to think that someone would see the name at 14 and start using it their whole life. iconic. she had nothing to worry about with that attitude; she never had the chance to be normal.