As much as I hate 1xbit, I don't agree with your proposal. If scams aren't moderated here, why we should ban 1xbit? It would be double standarts and people would start asking why other scams aren't banned.
But it's good point about spamming. I rarely can see good posts made by 1xbit participants. Maybe it's not worst kind of spamming, but they don't contribute much here. Though, I'm not sure that their content is bad enough to ban signatures