While the current prompt ("One-time password (OATH) for ...") is precise it would be nice to override this prompt with something more generic (such as "Validation Code:"). 

From a security standpoint this also provides an additional layer of information hiding.  While not providing any real security, a clean non-descript prompt does cover up the source of pam_oath.  This also allows for pam_oath to be dropped in as a replacement for Google Authenticator without any impact to end users (and the "why's the prompt different?" discussions).

Perhaps an additional variable that can be passed to pam_oath.so? (prompt="...")