As a follower of Marx, Che Guevara knew that the working class will always use whatever is relevant to its time and condition in its struggle against capitalists. T-shirts are the new literature, a new pamphlet, a way to convey solidarity and a way to educate and inform.
Don't be misled by ill-informed people who suggest Che or any other past Marxist would "kill you" or be offended by their images on a shirt or any other object.
Do try to honor Che's memory by buying a shirt through a poster or t-shirt collective.
"If you tremble indignation at every injustice then you are a comrade of mine." - Che Guevara