That showed up at the 1999 SHOT Show, its a customized SW 357 revolver made for the european market, around the same time Walther and SW agreed to co-offer the P99.
From Walther:
"Walther and Smith & Wesson have cooperated in the development and production of an advanced revolver design for self-defence - the Model R99. Sold with two interchangeable backstraps, the R99's Duo-grip adapts the gun to different hand sizes, for and improved hold and maximum comfort even during extended shooting sessions. The optimum balance of energy/accuracy with carrying comfort is reached for the .357 Magnum cartridge by the 3" barrel.
The R99 is available in sand-blaster matte blue finish and stainless steel. Design and distribution: Carl Walther GmbH/Germany Development and production Smith & Wesson/USA."