Mystery solved
One of my friends made this shirt for my friend who ended up wearing it
I didn't bring a sign but I got one from the ACLU, so that was nice.
eta: I didn't take this picture but just happened to come across it and it was my favorite sign I saw today (several times... the guy and I were in sync)
In Mass, a lot of our road signs look like that, so it was a nice, local protest sign with a good message