Future - 8:19 pm on Oct 2, 2010 (gmt 0)
We have added few customizations for our forum scripts and run this scripts once every week.
a. We check users signatures for SPAM every week, we find a user idle registration and after several weeks replace with a link in there profile or replace/edit the signature with leaving a link.
We check all signatures for spammylinks once a week and auto-delete them against our db of spam keywords. (a manual review is the only option available for us)