German Stainless Steel

Bruce and Eric are right...GSS stands for German Stainless Steel.  Theoretically, in the old days (1990's) players felt that this type of soft stainless steel had a more muted sound which gave it a more softer sound/feel than SSS or Surgical Stainless Steel which most of Scotty's putters are made from.  

In the end on the Super Rat's which are made for tour, the insert of GSS is meant to show off the metal.  However in most of the GSS Putters, even the Newport 2's that Tiger used back in the day, go for $7,000+ because of the expensive nature of the metal itself.

Hope that helps! Enjoy!  Love the Putter!

I don't think SSS stands for Surgical Stainless Steel. The story I heard is that there were people adding a G in front of SS to try to sell them for a premium on the secondary market, so Scotty started adding another S to stop this.  

Yes, it means German Stainless Steel and is used on some of Scotty's high end putters.