PS

If you like, see Peter Sidwell

Alternatively, a post-script, an afterthought, a written exemplar of l'esprit d'escalier, perhaps. Or maybe the postscript programming language, used in printing, typesetting and computer graphics.

Adjoined to a single character, this may denote a gaming console produced by Sony - the --1, --2, --X, and soon the --P. In this case, it stands for Playstation.

Could denote the image-tweaking software Photo Shop. - or potentially, abbreviate that apparently-oxymoronic field of academia "political science".

In Europe, is not unknown to denote the Parti Socialiste, or the Partido Socialista.

There is also PS Publishing.