The thing about blood type is that no US medical facility will give you blood based on a tag, a tatoo or a patch on a uniform. You get typed and cross matched or you get O- if there is no time. I was an Army medic. Soldiers put their blood type on things for style points.
I still wear my tag because it has my name on it. I figure that is all anyone would need to eventualy figure out who I am.
Medical people will however honor an alergy tag.
leo