This is coolbert:
From the Chicago Tribune today copied in entirety:
"Chicago Tribune PERSPECTIVE"
"10 things you might not know about TATTOOS"
# 3 "The fear of nuclear attack during he Cold War inspired officials to call for every American to be tattooed with his or her blood type. Chicago civil defense leaders said they favored tattooing on the left underarm rather than on the legs or arms, which might be blown off in an atomic blast. When the Tribune's 'Inquiring Camera Girl' asked people about the idea in 1950, the paper printed five responses, and not one opposed the notion. Law student Francis O'Byrne said: 'I think the tattoo should be put in the a less conspicuous spot than under the army because many women will object because of strapless evening gowns.' The blood type tattoo idea never really took off."
German SS mann during the Second World War [WW2] also had their blood type tattooed under the armpit. Which arm I am not sure.