Teddyboy As has been mentioned the warning levels as well as their display by your name and avatar is the default in myBB. We simply neglected to remove it from being shown.
As far as what would get someone a warning, not following our limited rules can result in a member receiving a warning. Action taken would be discussed among the moderators as to what if any action would be taken.
I can't think of any other board which explicitly states what will get someone a warning from a moderator and what action would be taken under all the different variables which could lead to a PM from a moderator. The warning system as used by most boards is simply a way for moderators to make a note for reference (e.g. as a way to see if someone keeps getting PMs over the same issue).
Here's the link to our very limited rule set in case you missed it.
http://damnfineshave.com/announcement-site-rules
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Doug
Careful, man, there's a beverage here! - The Dude