I believe most were export guns, sent to Wischo in Germany, which probably speaks to not seeing many here in the US.
My three inch was marked as "357 Security Special" on the sideplate which was one of the model names that Wischo had in various barrel lengths.
My 4" CS-3 never left the states and is not marked. The finish on both is the frosted bead blast finish as with the CS-1.
As for differences, just think of the CS-3 as being the next engineering change to the original CS-1, the only visible differences would be the squared off extractor star due to the use of CNC milling, and the biggest change from the noteworthy CS-1 is the front sight width change to 1/8" wide versus the original 1/10" for the Customs guns.
The bottom two revolvers in this pic are CS-3 models (both have the front sight changed to the Patridge style, by me)