OK, Jeansy, I looked through about 100 different Huey links and couldn't find a single pic of that placard being fully readable. I did see alot of pics of that paint job in which it didn't have the placard.
I believe the placard had to do with warning the student aviator that flight with the cargo door was prohibited, and must be verified fully closed before flight. It's no problem if it's not in your paint, I appreciate your efforts.