Official MUTCD Compliant R1-1 STOP Signs. Heavy Gauge Rust Free .080 Aluminum STOP Signs. High Intensity Prismatic (HIP) - provides higher levels of retroreflectivity versus engineer grade and standard high intensity. Where high intensity uses encapsulated glass beads, HIP uses prismatic technology to provide increased retroreflectivity 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 retroreflectivity. HIP STOP Signs are rated ten year reliability.