I bought it used on ePay about 10 years ago. The glass lens was broken into 2 pieces, but all there and the brass outer ring holds them in place nicely. There are NO markings of any kind on it. It is very heavy for its size. I'm guessing 30s or 40s, but it's just a guess. I painted the inside white to make it brighter and connected it directly to the brake light switch.

'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.