This is a Truglo Sight known as the Brite-Site, model TG131ST2.
When you need to make a fast and accurate shot" brightness counts. We brought fiber-optics to the shooting sports industry years ago for this very reason. We have now paired them with our tritium night sights to create a consistently bright sight picture-day or night! Our patented combination of Tritium and Fiber-optic technologies unites the best of both worlds. Whether you are in glaring daylight or complete darkness" you can count on TFO(R) to provide a bright and reliable sight picture.
Features:
Green front and rear
Unbelievable transition through all light conditions
Glows in the dark
Concealed fiber cannot be seen by target
Fits standard holsters
Snag-resistant design
Sig #6/#8 set