Smartsign S-6091-AL-10 Aluminum Sign,"Caution: RF Microwave Hazard", 10" x 7" Heavy-duty, 40 mil thick, rust-proof aluminum. Made of 96% recycled materials Durable, plastic laminate protects against weather, abrasions, and chemicals 4 mounting holes for screws or nails. Rounded corners for longer life and simple installation For indoor or outdoor use