I wore a green tshirt in college right after I got back from VN that had a chicken's foot superimposed on the symbol, and the words "Footprint of the American Chicken" below it.
It wasn't too popular, but that wasn't why I was wearing it.
Another cool one back then had a top-down view of a B-52 on the "peace symbol."
Still, I fought for their right to use it, wouldn't want to live where they can't, and often appreciate the "heads-up" it gives me about people I meet.