Emergency Flash Lights?

Libby was driving down the highway when she suddenly got a flat tire. She pulled over and put out some cardboard signs of men in trench coats. She had them wired so that every time a car passed by the trench coats flew open and the men were flashing the passing cars. Well cars were backing up as far as the eye could see. Finally a state trooper came up and said "hey what's up with those cardboard naked men signs you have?" and Libby simply said "Oh those are my emergency flashers".