This is a common point of confusion for folks that aren't knee-deep in Smith & Wesson Performance Center pistol lore. The gun that BAM-BAM is talking about is the S&W PC SD-9, the "SD" stands for "Stocking Dealer", it was a special, short run of elite, high-end hand built and fitted all-steel pistols that were not sent to any distributor exclusively, they were offered to any basic Smith & Wesson stocking dealer that wanted to order one. We're talking circa 1994.
Three models were offered, all based on the 6906-sized frame but a steel frame rather than alloy. They were offered in 9mm, .40 S&W and .356TS&W. These are extremely rare pistols and NIB/unfired examples typically approach $3,000 in auction sales.
These elite pistols are not to be confused with S&W's early attempts at a polymer frame pistol to compete with Glock, called the Sigma and later adorned with SD-9/SD-40 model names, also including the SD9VE/SD40VE and variants.
It is confusing, but the polymer guns and these limited Performance Center pistols are as different as a 1979 Chevette and a Ferrari F-40.