Accountant-Man
Level 13

Google is your friend:

What does O/A/O mean on a check?
 
For what does the O/A/O stand? Answer: The most logical translation would be "on account of." It's likely that the remitter had funds owed to John Doe, and his widow, Jane, requested a refund payable directly to her. First published on BankersOnline.com 7/12/10.Jul 12, 2010
** I'm still a champion... of the world! Even without The Lounge.