Cognomen Sīn (Sein 
, Sin 
, Soin 
) , throughout the world, is a widespread surname. The family name Sīn is characteristic of Myanmar, where it is a common surname, Malaysia, and Macao (explore the name in all countries). Not in comparison with a country's population, it is the most numerous in Myanmar, Malaysia, and India. Very seldom, Sīn is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| Sein | India, Malaysia, Mongolia, Hong Kong, Myanmar |
| Sin | India, Malaysia, Indonesia, Hong Kong, Myanmar |
| Soin | India, Malaysia, Indonesia, China, Myanmar |
| Sīn | Algeria, Myanmar |