I should remind everyone (before they post) that doing something that has some effect is way better than doing nothing. This problem is getting increasingly worse and finding just 'decent' (less than than 'good') quality content is becoming increasingly hard. Tagging account sellers and sold accounts would have an effect on what they can do afterwards, because they would most likely be rejected by signature campaigns.

I wouldn't mind, but it isn't up to me. As a starting ban for a signature spammer 2 months or more seems fit.

This would not prevent account sales, as one could easily do it in private or on a external site. I don't see it being a bannable offense anytime soon (even though I would not mind it).