Courtesy of "Wiki Answers:"
At one time all Catholic nuns adopted a new name, perhaps patterned after a saint they wished to emulate and they usually took "Mary" as their second name. The practice of taking a new name is now optional, some orders continue it, but many do not, so its common now to see a name like "Sister Barbara Jones".
For me, that would clear up the "Sister" and "Mary" issues; I would treat them as I would "Miss" or "Dr." That is, it's not really part of their name, but I'm okay with it. As for their signatures, the UCC generally indicates the customer can sign her name any way she wishes. If their identification matched the rest of their name I would be satisfied and await with some glee the field examiner who would choose to criticize my decision in writing.
Shortly after CIP took effect there was a bank in Florida (Tampa?) that drew a lot of press because it refused to open an account for a nunnery that could not pass its CIP requirements. That's not a club I would want to join. To be fair, I've seen field examiners turn a blind eye toward CIP discrepancies based on religious convictions; e.g. the Amish. Occasionally common sense interferes with all of this stuff.