This is a TROY Sight known as the BattleSight, model SSIG-FBS-RTBT-00.
Troy Industries' Tritium BattleSights(TM) are designed to eliminate the poor sight orientation that is typical in twilight. Tritium is a form of hydrogen that emits a continuous light source when batteries or electricity are not available. The front post is centered between two Tritium points of reference to allow proper alignment. Troy Rear Folding Tritium Sights" a permanent" rail-mounted alternative to a standard A2 sight" allow limitless mounting options on all-length rails with a serrated ramp to eliminate glare.
Features:
Sight can be moved or taken off without permanent modification to the firearm
Features snag-free apertures at factory height
Front post is centered between two Tritium points of reference
Will not work with a railed gas block that is higher or lower than the receiver
Front sight must be mounted at the same height plane as the rear sight
