This is (was) a very handy protection for your grille against those big yank tanks. A light bump, and the "Sonic Shield" makes an internal electrical contact to blow your horn when a car ahead backs too close. It may work with modern plastic bumper cars as well. This accessory was sold in the fifties and sixties by MG Mitten from California (photo from the book "Accessories for your Sports Car" by Larry Reid, published by Sports Car Press, New York, 1958)