To add better night visibility to all trucks, Suburbans and panel trucks, General Motors offered a 4 inch diameter reflector as a dealer installed accessory. With the single small factory taillight, seeing of these vehicles on the road could be difficult especially if their one bulb burned out. To help correct this problem GM offered a larger reflector that could be attached to the rear license plate bracket. It greatly improved visibility to others at the rear during night driving.
This was a time when town street lights were limited. Of course, on the open road these were no lighting along the highways! This simple GM reflector was offered by the dealers to prevent rear end accidents. The customer could buy this dealer accessory from about 1940 through 1953. One of the attached photos is taken from a 1949 Chevrolet Truck Data Book. The 4 inch lens is a Stimsonite # 24 and the metal Guide ring has a stamping of X-19.
Jim Winters of Rochester, Minnesota has both a restored 1946 panel truck and ½ ton pickup. He found these reflectors for both his vehicles at local swap meets. Few people recognize what these reflectors were used for. Jim found his in a box of miscellaneous unmarked parts.