Surname Sai' (Sein 
, Sīn 
, Sai' ) , all around the world, is a common family name. The family name Sai' is characteristic of Myanmar, where it is a common surname, Mongolia, where it is quite a common surname, and Estonia. Measured by absolute frequency, it is the most numerous in Myanmar, Malaysia, and Mongolia. Likewise, Sai' is the forename as well as the last name.