If signatures bother you because you don't like to read the spam, ignore the users that you feel are posting only because they are paid. Then you don't have to pay attention to what they write anymore. You could probably get a couple hundred users ignored within a few hours if you put your mind to it.

You could also open self moderated threads if you are trying to have a serious discussion. Then you can delete posts you feel are off topic or irrelevant to the conversation.