Family name Sigþrúður (Sigþrúður 
) , all around the world, is an extremely rare cognomen. Much more prevalently, Sigþrúður is the forename as well as the last name.
Jónsdóttir, Harðardóttir, Þorfinnsdóttir, Sigfúsdóttir, Sæmundsdóttir, Elínardóttir, Rögnvaldsdóttir, Friðriksdóttir, and Sigurðardóttir