Well, the rule isn't banning advertising. It's just banning signing up for the sole purpose of advertising. One can post an s**** but be active in other topics as well. I don't think such a person would fall under the category of people who just signed up for advertising purposes
For example,
this user posted s****. However, looking at his previous posts, I find that it's a stretch to say that he signed up solely for advertising purposes. The way the rules are written as of now, the act of signing up is banned, not the act of advertising.