Tee shirt design

I'm interested in producing tee shirt designs. The concept is libertarian in messaging and classic Americana in design with a modern urban edge, perhaps even Marvel like. I've attached a few samples that caught my eye, and although none of them are exactly what I'm looking for they may be useful as reference points.
I'd like to begin with a single shirt design featuring the words " Free Speech" on the shirt front with the message " People died for your right to say stupid things." on the back. I'm thinking about a silhouette of World War 1 soldiers climbing out of a European trench as the graphic, but I'm open to suggestions if there's a better idea. My main concern design wise is that the entire shirt design, front and back be cohesive artistically, with fonts and design etc integrated into a single theme.