Sigma Filmproductions (Corporate Name)

Orlando, 1994: credits (Sigma Filmproductions)

OCLC, Oct. 8, 1997 (hdgs.: Sigma Filmproductions; Sigma Films; Sigma Films Amsterdam)

Guide du cinéma européen, 1989: p. 345 (Sigma Filmproductions BV; founded 1974)

Internet Movie Database, Oct. 13, 1997 (Sigma Film Productions)