What does the SSS stand for in the name of the Nissan Bluebird SSS Turbo? Super Sports Sedan?
Nissan Bluebird SSS Turbo Super Star
According to this 1981 JDM commercial it is Super Star! (Sedan?)

You can watch the advertisement below:

Personally I prefer the Super Sports Sedan. ;)

Direct link to video: 1981 NISSAN BLUEBIRD Ad (HD)