I think deleting the offending posts and/or messaging them a warning that if they continue to post crap at their current rate they will be banned will be a stern enough warning. If they're having their posts actually deleted then this will obviously make them step up their content as it's not worth it to them and is actually counter-productive to keep doing so. If after a warning they continue to act the same then give them a weeks ban as punishment and then they should get the idea. Like you said, many don't want to risk their accounts as they are valuable to them so banning outright, especially without a warning (if you didn't give them any other warning), should be a last resort and could probably be avoided in most cases.
There's too many to delete posts one by one, it takes 3-5 seconds to delete one post. Deleting posts in threads is different because there is a quick moderation option available via checkboxes and they can all be deleted at once, this isn't possible on a users post history page, has to be done one by one. PM warnings are useless in my experience and you just end up in circular arguments. The week ban is the warning.
BadBear, we obviously have a different opinion on signature campaigns but I'm perfectly fine with that. I won't go far supporting my opinion and I also appreciate that you're here explaining what is happening and giving us some insight. But honestly, what's to earn out of giving people the impression there is a "risk to get banned"?
Well it's our only option at the moment, besides just let it continue. if this doesn't work then we'll need to explore other options, such as disabling sigs, not allowing links, or filtering links from services such as the ones who buy signature space for ads.
A handful of people probably already got banned. And this happens while a nother handfull of people is having a daily three digit post count.
I'll get around to them eventually, I have a whole thread dedicated to maintaining a list of these folks with input from all moderators welcome. Also have users pm'ing me with suggestions, a lot of people are sick of this.
Do you think that the ones that got banned are going to come back and never spam again in fear of not getting banned again?
It takes at least two months to get an account worth selling signature space on, I'm pretty sure it'll work.
According to my humble opinion again you should At least let them know why they got baned in more detail. Let them know specifically what post of them was it that you didn't like. Don't just press the "ban button" without getting into the effort to explain why the user got banned. This is going to prevent people from being repeat offenders and also help make the situation more clear. You should do this anyway if you don't want people to come back at you complaining for an unfair ban.
Because to me, it seems normal to get complains if accounts get banned without any previous warning. (And no I don't think the posts you made as warnings are proper for this situation, it's so easy to miss one post out of thousands no matter how ipmportant it is.)
I haven't seen many complaints, just two people who didn't know how long they were banned for and why because I forgot to add the reason and duration in the text field (I pm'ed them when I saw their post). Most of these folks know full well why they were banned.