The regulation does not require you to perform CIP on mere signatories, only the customer. In this case, the customer is the corporation.
However, the regulation is no longer your primary source of direction. Your board of directors adopted a written CIP more than 18 months ago that sets out your bank's specific requirements. Your bank's CIP may enhance the requirements found in the regulation. Your CIP is the only reasonable resource to research for an answer.
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In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.