It looks like a Millett series 100 front sight, a ramp with a large base on it, held in place, basically, like a rivet with two legs. Milletts didn't come with a red insert (red paint was available) so someone did a fine job filing a notch and inserting a red plastic piece into the sight.
Milletts were sorta popular around here for awhile, when one of the local gunbutchers decided to "buy a franchise" and install a buttload of the things. He about went broke having to replace those front sights when they went flying off the pistols despite having those two "legs" rivetting the sight to the slides.
Yeah, I had one of those front sights installed on a BHP, and yeah, I was one of the guys who's front sight went a-flyin', and yeah, I hate anything Millett sells, to this day.
