May not be %100 but it is one factor, of a few, to access when you can't get your hands on the item before purchase. Sure there may a few w/o the "A" but I won't gamble on them unless I can hold them first or they are from a trusted member that knows the history on them.The early rep samples and production pairs of the Pit Boss did not have the ‘A’ on the arms. That is not necessarily the best way to tell a fake.
