fire inspectors association of indiana

I've been in the process of getting our on-site fuel tanks switched to the NFPA 704 compliant marking, per IFC 5003.5. Currently, the majority of our outdoor tanks have DOT placards on them, which I consider appropriate for vehicles, but does not meet code for stationary tanks. 

Is anyone else enforcing this? I've contacted a couple of suppliers to make them aware, but I have the impression this issue hasn't been raised much.