The issue is that these two sites have not scammed yet. While I am confident that both of these sites will scam, IMHO I think pre-emptive actions are unfair.
Regarding the signature ads: The exchange is for displaying an ad. The exchange does not involve you astrosurfing or defending them. Why not continue to carry the signature, but add a visible disclaimer? You have a free line.
So you will add neg rep to all? Better start working on the list then; you will take a few days

Since you neg repped him, you should also do to the two escrow providers, as they asked to revert back to original sig, and also all the other carriers who are aware.
He can't add anything else in sig as it contravenes rules, but yeah, he can add a message after each post. Will require a bit more work on his part.