Well, I don't know about the Model 66, but I'm sitting here looking at an early Model 67 in the 5K22XX range, and both have an "S" stamped in them. On the trigger, it is on the backside of the finger curve, up high near the juncture of the trigger body where it meets the finger curve. It is right where the trigger stop would meet the trigger. The hammer is stamped "S" on the underside (not visible unless the side plate is removed. If you take the sideplate off, it is directly above the stirrup, on the flat surface. I don't have my SCSW here (it's at work, anyone have one handy?), but I'm pretty sure this is an early one. I acquired this gun in the early 70's. It is not a target hammer or trigger.
My old armorer declined to do any trigger work on it, because of what he said issues with working on stainless.
Years later, when I went to Armorer's School at Springfield, they advised that they had subsequently gone to Flash Chromed triggers/hammers.
FWIW