The name Sinjin is a boy's name . Sinjin and is often added to lists like TV Character Names and discussed in our forums with posts like "Love, Like, Lose -- Outlandish/Guilty Pleasures edition!".
From the experts:
The name St. John is much more usable and exotic in its phonetic spelling--similar to the way St. Clair evolved into Sinclair. St. John has some literary cred--St. John Rivers is a cool character in Jane Eyre.