An application for service retirement can only be withdrawn by filing a written request to withdraw such application with the Retirement System prior to the effective date of retirement. This written request must be signed by the member, or if he is incompetent, by his spouse or the committee of his property, or if he is a conservatee, by his spouse or the conservator of his property. Such written request will not be considered filed until it is actually received. However, such a written request will be deemed filed on the date it is mailed if it is mailed to the Retirement System by United States Postal Service certified mail, return receipt requested and is actually received by the Retirement System as the result of such mailing.