I was searching Ebay just now and ran across this 1924-S Peace Dollar which grade is being described as AU/BU. I dont know what his meaning of AU/BU is but it sure doesnt come from any grading guides I've ever seen. BU must mean "beat up" in this case. Check it out......Ebay item#260141122344.
AU: Agonizingly Unappealing BU: Butt Ugly I would rather be eaten by a werewolf than use the silver to kill it.
I think the grade may have referred to the seller's fingers cuz it sure as heck couldn't have been that coin!