ADS is spot on.
In view of the recent outbreak of trouble from several idiots we upgraded to the new version of the forum, which gives the Moderators greater control over troublemakers. So in my absence they are able to control / limit / ban the postings of any troublemakers.
The warn facility is there to enable Admin or Moderators to warn a member for any breach of the rules. The facility informs me and other mods of any problems, or warnings that a member has recieved. Three warnings, and the forum will automatically suspend the member for "X" number of days. Upon making a warning to a member a moderator also has to fill in the reason behind the warning, which is then emailed to the member concerned and the Admins.
The warning appear as a bargraph under each members name, on this forum, one warning will equal around 33.333% of the bargraph display. Reach 100% (and there is no reason why any member should) then a suspension is in place. The warnings can of course be retracted by Admin should it have been given unfairly.
This is a vast improvement over the immediate ban that I used in the past, and allows newbies to make small mistakes and be directed to the forum rules, without being banned immediately as in the past.
Each member can view their own warning levels, but not each others. Admin & Mods can view the levels of every poster.
Of course there will always be people signing up for the wrong reasons and getting banned. It's happened several times in the last week, especially one who chose to send harrassing P.M's requesting a date to each female member

then the MP3 spammer turned up....these are just some examples!. Happily, most of the general membership will never have concern to worry about the warning system.