Correct me if I am wrong and specific signatures can easily be detected and removed.
Simple - ban signatures that link to 1xbit site(s).
If a gullible victim doesn't see the ads here, they'll see the same ads at Blockchair or Coinmarketplace. "Be your own bank" means you should "use your own brain".
I would argue that we should use our collective brain and realize that allowing such malicious scammers like Yobit (which did happen) and 1xbit (which didn't for some reason) to continue screwing with this forum has no upside. They are not here to discuss Bitcoin, they're here only to spam the shit out of it. And we're pretending that rules are set in stone and there is nothing anyone could possibly do because rules and regulations don't allow it. Doesn't get much more snowflaky than that.
BTW theymos the hands-off guy did ban 1xbit from buying forum ads so there's that. He also e.g. bans users doxing him but not
users doxing other people with no trade disputes. So there's rules and there's different rules.