Create topic in meta, report them to moderators, leave them neutral tag in case moderators don't take any action against those accounts and don't break your head too much over it. IIRC, I was giving negative feedback to ban evaders but lately I am giving them neutral feedback.

Actually, it doesn't make much sense to me, forum administration ban someone, they create new account, you expose them and all of sudden they are allowed to post again. Why not unban banned account then?  It's like account is banned, not the user.
Some campaign managers simple don't care who is advertising project, they only care that signature is visible and someone will see it and click on it.