If anyone tries to say he broke the law by taking their sign, who broke the law first? They were standing in the middle of the street intentionally blocking traffic.
It was good to see another citizen take action, like those commuters who dragged those Extinction Rebellion protesters off the top that train in the London Underground did the other day. If more people did this, and the cops cleared the streets so that right-of-way was observed, we wouldn’t be seeing those cowards do this kind of thing. I loved how they all ran off when he came back to engage them in “conversation.” ;-)
You want to protest? That’s fine? Do it in a lawful manner and obey all the same laws we routinely do. But when you start preventing others from going about their lives, preventing them from getting to work or school or whatever, then don’t be surprised when you get a little blowback.