This is a Truglo Sight known as the Brite-Site, model TG13SG2PC.
They created the original TFO(R) day / night sight" then made it virtually indestructible with their hermetically-sealed TFX(TM) sights. Now" they are taking TFX(TM) technology to the next level for professionals and shooters who demand maximum performance from their handguns-providing ultimate reliability" accuracy" and brightness no matter how tough things get.
Features:
Contrasting colored front sight ring for even faster focus
Quick and accurate U-notch Design
Angled rear sight edge for emergency one-hand operation
Sig #6/#8 set