If the company where the investment accounts are held is a NYSE member, they would have to follow this rule. I don't think that this would impose any requirments on you. I would speak to the company and clarify what they are asking for. If they are asking for the typical "407 letter" (our employee has our permission to hold this account at your firm) I have found that it is easier to send the letter than to try an convince them you are not required to comply with this rule.
If you have any doubts or concerns, please consult your attorney.