The application on IRS form SS-4, together with any supplementary statement, shall be prepared in accordance with the applicable form, instructions, and regulations, and the data called for shall be set forth fully and clearly. The application shall be filed with the service center director serving the internal revenue district where the applicant is required to file returns under this subpart, except that hand-carried applications may be filed with the district director of any such district as provided for in 26 CFR §301.6091-1. The application shall be signed by:

(a) The individual if the person is an individual;

(b) The president, vice president, or other principal officer if the person is a corporation;

(c) A responsible and duly authorized member or officer having knowledge of its affairs if the person is a partnership or other unincorporated organization; or

(d) The fiduciary if the person is a trust or estate.

(75 Stat. 828; 26 U.S.C. 6109)