A way that those suckers still stuck in that shithole could fight against this spam from within Reddit would be hostility. Basically: if someone mentions a brand, you tell them to sod off, call them a spammer, associate the brand with dead children, etc. Then the smart move from the advertisers’ side would be to avoid being mentioned in Reddit.
Of course the suckers won’t do it though. Any Reddit user with a shred of self-respect and willingness to fight against the sorry state of the platform already left it. Or at most interact with it passively.