I Googled: " Fold down bumper guard" images and there were a few pictures of almost identical guards as your picture. Looks like Pre '68 Dave is correct, I had never heard of them before.
1946 Chev 1/2 ton - 6V/+ground/Bias-ply original - shake/Rattle and Roll! (SOLD) 1940 Chev 1/2 ton Franken/Restomod
I have one on my ‘41 Chevy coupe rear bumper to protect the trunk handle. It was an option back then. Have no idea why someone would put it on the front of a truck.
Chuck 1950 Chevy 1/2 ton (all original) 1951 Chevy 1/2 ton (future streetrod) 1941 Chevy coupe 1938 Chevy coupe streetrod