Abstract: A method of providing a user controllable sign, on the trailer of a tractor-trailer rig. The tractor includes a cab and the trailer is electrically connected to the tractor by way of a jack that provides a set number of electrical connections between the tractor and the trailer. The method begins with the installation of a manual input device in the cab. This device creates a signal that can be overlaid on a jack input without disrupting the input and is electrically connected to a jack input. Also, a signal receiving unit is installed in the trailer, and is connected to a wire electrically connected to the jack input that receives the user signal from the manual input device. This unit is able to determine the presence of the signal from the manual input device. Also installed in the trailer, is a sign deployment controller that is at least in part responsive to the user signal receiving unit. Finally, a sign assembly, controlled by the sign deployment controller, is installed.