What’s a Motto?

As a new paratrooper, I was struck by all the T-shirts on base emblazoned with the motto "Death from above!" Later I noticed a submariner with a T-shirt that declared "Death from below!"

Then, standing in line for chow one day, I was served by an Army cook. His T-shirt had a skull with a crossed fork and spoon underneath and yet another warning: "Death from within!"