"Stop - Slow" Double Sided Paddle By SmartSign | 18" 3M Engineer Grade Reflective Aluminum 3M AUTHORIZED. Authorized signs are certified to the 3M Matched Component System. This assures that signs are durable outside. DURABLE ALUMINUM. Signs use 3M reflective Engineer Grade film mounted to non-rusting aluminum and last up to 7 years outside. Signs are 118 mil thick and unlike steel signs, our aluminum signs do not rust. EASE OF USE. Signs come attached to a 5" all-weather foam handle at the bottom of PVC Handle for easy gripping. STOP-SLOW PADDLE. These double sided Stop-Slow paddles are great for school crossing guards and helps prevent accidents.