engine size emblems below front side marker lens, what is correct?

[sircrunch]

Looking around at pictures all over the internet, I'm seeing some trucks with the "8-350" emblems for instance, under the front side marker. But most pictures I see, the truck does not have these. And I can't find any rhyme or reason (year, trim level, engine type etc) as to why these truck have or don't have the emblem. What is correct? with or without? I have a 70 c10 short stepside that has a 350 in it now. It originally was a 6 cyl I think. It does not have the holes in the fender for these emblems. But I found some new emblems at the swap meet and I'm not sure if I wanna use them or not.