The return of a corporation with respect to income shall be signed by the president, vice-president, treasurer, assistant treasurer, chief accounting officer or any other officer duly authorized so to act. In the case of a return made for a corporation by a fiduciary pursuant to the provisions of section 6012(b)(3), such fiduciary shall sign the return. The fact that an individual's name is signed on the return shall be prima facie evidence that such individual is authorized to sign the return on behalf of the corporation.