Surname Sijak (Sijak 
) , throughout the world, is a rare cognomen. The last name Sijak is habitual in Serbia, where it is quite a rare surname, Austria, where it is a rare surname, and Malaysia, where it is a very rare surname. Measured by absolute frequency, it most frequently occurs in Serbia, Indonesia, and Germany. Much less frequently, Sijak is the forename as well as the last name.