This is also done with signatures. One can’t have a signature for a certain amount of time (a week I think) and with less than five posts. But even more, this has changed in that you fellow members can influence this yourself by demoting new members (using the reputation system) who behave suspiciously. Members with negative reputation can’t add a signature. Of course, this has to happen before
they have a signature.
Refer to this thread: http://www.codingforums.com/showthread.php?t=289665