I can suggest something like the BLM raised fist, it is used mostly around BLM but I think it’s a good symbol for activism as a whole?
Something like this: https://stock.adobe.com/nz/images/black-lives-matter-fist-hand-graphic-icon-symbol-black-power-illustration-perfect-for-a-protest-sign-card-or-shirt-design/366822987
Makes sense, I do prefer clean black/white designs, but this is a personal preference and I see how multicolor icon with multiple people/fists is better representation of the community.
i think that website allows just the outlines to be used as well, if that’s what folks prefer!