You are wrong.
Signs, people and material, if done right, can educate passers-by. You may dislike my fact, but it is the truth.
Admittedly, many people have their minds already made up. For those on the fence, or possibly not aware because of their own daily lives, it is a way to show unity, and positions. Having printed material handy helps reinforce the position.
Based upon much experience.. YMMV
Btw: I used to sell tie dye t-shirts in LA many years ago. It was both profitable, and fun :-)
"What if the American people learn the truth" - Ron Paul