Really odd marking on bed

[NevadaDVX]

I found a decent used bed for my customers truck since her floor was rotted out. I noticed the front panel has a strange marking that came from the factory. I know it came from the factory because this bed is original paint everywhere. You can see in the pic that the black line that makes up the lettering(?) was painted over and has sags of paint under it.

I'm not sure what year the bed is, but it's going on a '71 and is a long bed. Just wondering if anyone has ever seen anything like this. Small talk on a Sunday evening.