This is a Hi-Viz Sight known as the Litewave, model MPSLW11.
HIVIZ(R) LiteWave(R) Rear Sight for Smith & Wesson M&P Shield pistols. Fits Shield models in 9mm" 40 S&W" and .45 calibers. Includes Green" Red and Black replaceable LitePipes.
Features:
Interchangeable Litepipe rear sight
Includes green red and black LitePipes;Factory height rear sight .140 wide notch
