I'd be willing to bet it's a Standard Automatic Pistol and not a Mark I..... that sight is too low for a Mark I. Besides - who would replace a Mark I sight with something like that?
It's a MKI Bull Barrel. I know it's aftermarket but just trying out maker. I beleive it is an older sight. I was wondering if it was ever used on a Clark gun.
Looks almost like a modified old Colt woodsman rear sight or such, by the screw..........picture is indeed a tad blurry ,OR a High Standard even.....
yes, it appears to be a 'standard auto' as said above ( markings on the right side of the receiver tube)