Across the world, Сейн (Sein 
, Seyn 
, Sejn 
) is a common largely male, but uncommonly girly first name. The forename Сейн is habitual in Mongolia, where it is a common principally male, but scarcely girly name, Myanmar, where it is quite a rare dominantly masculine, but uncommonly female name, and South Korea, where it is quite a rare gender-neutral name. Likewise, Сейн is the last name as well as the forename.
Сейн is also a name for the fictitious and mythical characters: sein Vetter , the operatic character in the operetta Abschiedswalzer; Sein Sekretär , the operatic character in the opera Der junge Lord; Sein Jünger , the operatic character in the opera Der Golem and Sein Schneidermeister , the operatic character in the opera Kleider machen Leute (Zemlinsky).