It's a Liberty Bell Mfg. Co. Swainsboro, GA. driveway signal model no. 56.
There's 2 currently on Ebay. It, unlike most driveway signals has the parts all visible mounted on a steel plate. The left half has the bell assembly and the right half has the transformer on top and the half moon sphere covering the air pressure switch beneath it. The air hose nipple is on its bottom.
Thanks Jack.