There is really almost no valid reason for one to sell their account here. Even if they were desperate for money, then the best thing to do would be to put it in as collateral for a loan.
The account only has value as collateral if it can be sold. And if that's the "almost no valid reason" you mean, it could also be abused to sell an account: take a fake loan, default the loan, sell the account.
I'm not sure about that, nor what other moderators/administrators think. Currently, banned users get stripped of their signature and other profile information (implemented sometime in 2016 IIRC).
I would suggest a Rank: "Banned". One word, right under the username. It can even be a warning for other people.