Official MUTCD Compliant R1-1 STOP Signs. Heavy Gauge Rust Free .080 reflective Aluminum STOP Signs. High Intensity Prismatic (HIP) - provides higher levels of retro reflectivity versus engineer grade and standard high intensity. Where high intensity uses encapsulated glass beads, HIP refelctive metal signs use prismatic technology to provide increased retro reflectivity levels four times brighter than engineer grade. HIP features 24-hour performance with increased daytime and nighttime visibility. Tougher topcoat provides improved scuff and scratch resistance and increased durability. HIP meets ASTM D Type III & Type IV specifications for retro reflectivity. HIP STOP Signs are rated ten year reliability.