Reflecting on what I found while Googling, I think the phrase “XKCD protest” refers not to a protest portrayed in an XKCD comic but rather to an XKCD comic that was used in a protest: https://www.reddit.com/r/xkcd/comments/6uu5wj/xkcd_1357_in_the_boston_protest_xpost_rpics/
Reflecting on what I found while Googling, I think the phrase “XKCD protest” refers not to a protest portrayed in an XKCD comic but rather to an XKCD comic that was used in a protest: https://www.reddit.com/r/xkcd/comments/6uu5wj/xkcd_1357_in_the_boston_protest_xpost_rpics/