Nanuk - that's what I'm talking about. More info on them? Where did you get them, etc.
AFAIK the topstrap and barrel of the M640 Pro and the hammerless version of the M632 (sku# 178046) are specially dovetailed to accept standard M&P sights. I've not seen this verified in an official press release or anything, but I remember some folks on the S&W forum saying that these revolvers come with the same sights that are used on the M&P9/40c.
The dovetails are visible in the profile view of the M632 on the S&W website:
I have no idea what it would take to install these on a revolver designed to take a standard S&W target sight base. The sights referenced in Alnamvet68's post or a set of Cylinder & Slide "Extreme Duty" sights would probably be easier to install.