This is a Trijicon Sight known as the Bright & Tough, model GL201-C-600651.
TRIJICON SUP NS GRN FOR GLK 9MM YELL: Trijicon Bright & Tough(TM) Night Sights are three-dot iron sights that increase night-fire shooting accuracy by as much as five times over conventional sights. Equally impressive" they do so with the same speed as instinctive shooting - and without the need for batteries.
Features:
Tritium-Phosphor lamp
Sapphire window
White rings
Silicone rubber cushion
Protective aluminum cylinders
Suppressor sights
Back up iron sights
