This is a Hi-Viz Sight known as the Litewave, model HRBLW01.
HIVIZ(R) LiteWave(R) Front Sight for Ruger Mark I" II" III and IV steel bull barrel pistols. Also fits: Ruger 22/45 with adjustable rear sight (does not fit the 22/45 LITE); Ruger Single-Six revolvers with adjustable rear sight; Browning Buck Mark pistols (does not fit the Challenge" 5.5 Target" and 5.5 Field). Includes Green" Red and White replaceable LitePipes.
Features:
Interchangeable Litepipe design
Includes green red and white LitePipes;Front sight