I like the price and it is really pretty. But O/S? I've never heard of that in a 81. I know there are O/Os for that year. I wonder if it is a VAM5 and the seller thinks that is a S instead of an O. (edit... shoot.... I see you put VAM5 in the OP. Nice call) http://ec2-13-58-222-16.us-east-2.compute.amazonaws.com/wiki/1881-O_VAM-5
It looks like the seller put that sticker on many years ago when Breen called it an O/S. I know PCGS labels them "So called O/S".