Sigismund is a common name.
Sigismund of Burgundy (Saint Sigismund), king
Sigismund, Holy Roman Emperor, also king of Luxembourg and of Hungary
Sigismund of Austria
Sigismund of Bavaria
Sigismund I the Old, King of Poland-Lithuania (1506-1548)
Sigismund II Augustus, King of Poland-Lithuania (1548-1572)
Sigismund I/III Vasa, King of Sweden as Sigismund I(1592-1599), King of Poland-Lithuania as Sigismund III (1587-1632).
Sigismund Bathory, prince of Transylvania

The name of Siegmund, a focal character in Wagner's Die Walküre, may be related to this name.