You cannot treat a Ponzi scheme to pedophilia or murder for hire, that's an abusive analogy
Why?
If the advertisement says nothing about the person that chooses to put it in their signature space, then why does it matter what they put there?
If it does say something about the person that chooses to put it in their signature space, then clearly the following aren't true:
A person's reputation is not what is in their signature line . . . Having a paid signature is nothing more then receiving money for advertising a good or a service
The only thing that these people are saying, by accepting to rent their signature space, is that they need the money. Nothing else.
I would say that common sense would dictate that advertisements are not endorsed by these channels of information
EDIT: unless you personally endorse something you are not "signing" your messages with a specific advertiser
You can't have it both ways. Either your signature has an effect on your reputation, or it doesn't. Which is it?