Abstract: A bifurcated mounting bracket for a caboose replacement signal transmitting unit straddles the coupling knuckle of a rear train car and is secured to the knuckle by a lower end pivoted hasp which is padlocked to the bracket. Depending and upstanding teeth on the bracket and hasp, respectively, positively engage top and bottom surfaces of the coupling knuckle with minimized metal-to-metal contact. The signal transmitting unit is supported above the elevation of coupling crowns to avoid destruction. The mounting allows the coupling of another car in the train behind the car on which the signal transmitting unit is mounted without destruction of the unit or its mounting.