Three PSG's:

PSG is a Breton acoustic guitar trio consisting of Patrice Marzin, Soïg Sibéril and Jean-Charles Guichen. A former member is Jacques Pellen. See also: Marzin Sibéril Guichen

There's also Finnish alternative rock band called PSG. http://www.myspace.com/psgbandfin

Furthermore, there is one Japanese group of this name. The group describes its
sounds as dark, deep and calls it "All Downer Freaks" or "All Trips" music.
Their friend edited image movies from "TAQB" (EP). So wonder you all would enjoy not only music but also movies with Deep, Dark Feelings. PSG would like to listen to the deep n' dark sounds fans who are finding such sounds, and hopes to add on one of your new favorites. Enjoy it in Your Deep N' Dark Sides with PSG.