Use this flashing triangular vehicle sign to warn oncoming motorists you are delivering mail and making frequent stops. The two flashing lights are visible from both front and rear, and reduces the risk of rear-end accidents. The unit easily and securely attaches to the roof of any vehicle with four powerful magnets, and are powered by a 10' cord and 12VDC (cigarette lighter type) plug with built in, replaceable fuse. It's recommended not to drive over 35mph with sign attached to outside of vehicle. Ships USPS Insured.