For meetings of the commissioners of the sinking fund pertaining to obligations, each of the commissioners may designate an employee or officer of that commissioner’s office to attend meetings of the commissioners when that commissioner is absent or unable for any reason to attend and such designee, when present, shall be counted in determining whether a quorum is present at the meeting and may vote and participate in all proceedings and actions of the commissioners pertaining to obligations, provided, that such designee shall not execute or cause a facsimile of the designee’s signature to be placed on any obligation, or execute any trust agreement or indenture of the commissioners. Such designation shall be in writing, executed by the designating member, and shall be filed with the secretary of the commissioners and such designation may be changed from time to time by a similar written designation.