Each list has it's own "Posted Message Footer" and "Posted Message Header". These are generally blank by default, but if you've upgraded, those messages may have carried over. To edit them, log in as the Domain Admin and go to the Mailing Lists area:
Settings --> Domain Settings --> Mailing Lists
Find the list whose footer you want to edit and click on it. Once the List Options load, go to the Messages tab. Look for the "Posted message footer" message and click on it. You can then edit it as needed. As an aside, there's a "Digest footer" as well for digest messages. That's separate from normal list messages...
I hope that helps.