I like the idea of saying that protests are signals. It corresponds with Spence’s definition of signals. The costlier a protest is to organize, the more value it should have in the eyes of third parties. I also like thinking of protests as signals because it suggests that protests are informational. One of the main functions of protests is to communicate new information about a social issue to a broader public (even if only to let others know that some people are really pissed off about this issue!). If you just can’t get enough of protests (and believe me, I understand the fascination), I wrote a post addressing this question a few months ago.
A nice one (and at the right moment too!)