They are on the third generation/version I believe. However that is technically speaking. They dropped the Sigma name in the SD series. Two generations previously carried the Sigma name.
They even had compact models. The older SW Sigma line had a 4.5" barrel they all are 4" now. Even had a ported version. Never know what you can dig up!
The newer SD9VE has front and rear slide serrations, Rail mount, and I believe it is when they went to the 16 round Mags.
http://en.wikipedia.org/wiki/Smith_%26_Wesson_Sigma