Bo-mar tuning ribs were an addition to the top of the slide that helped control the barrel lock-up. They spanned the length of the slide from front to back. That added the extra weight that Scorch was referring to as a heavy rail, but that's not what you have.
You appear to have a rear sight for which the top of the slide has been relieved, as Bo-mar stand-alone rear sights required to achieve their low profile. That makes it a "Bo-mar style" sight in 1911 jargon, but there were so many knock-offs made that I don't know who your manufacturer was unless it's stamped somewhere on it. Could have been Bo-mar, but very well may not be. I don't recall ever seeing an actual Bo-mar brand sight with the front to back rib, but that doesn't mean there weren't any. I'm just not aware of them. Bo-Mar itself folded up after the principals died (2006 and 2007).
Front sight extensions for target pistols used to have longitudinal dovetails like that and worked fine, but they weigh a lot less than a rear sight. The potential vulnerability for one on a rear sight would be recoiling loose unless a set screw digs in somewhere. Sure looks nice, though.
Front sights being silver-soldered in place was a standard technique to answer the tendency of the traditional Colt staked tenons to come loose. The original Browning designed front sight didn't often do that because it is so small and light, but when target shooting caused front sights to get bigger and easier to see, the issue arose. They would get loose and wobble a little, enlarging groups, and sometimes actually fly off (which they would do almost exclusively in the middle of a match when the owner didn't have a back-up gun with him).
Silver soldering was the solution for a hardball gun. For a wad gun, getting a shallow longitudinal dovetail milled in the front of the slide allowed installation of an extended front sight that increased the sight radius for more aiming precision. Since then, mostly crosswise shallow front dovetails have replaced both techniques. The drawback to silver soldering is you have to refinish the slide afterward, which fewer shops are set up to do these days. It can add significant expense if the gun has to be sent out for that.
