Whenever under this Act or any rule, regulation or bye-law made thereunder, the doing of, or the omission to do, anything or the validity of anything depends upon the approval, sanction, consent, concurrence, declaration, opinion or satisfaction of the Commissioner ¹ [or of any municipal officer, a written document signed by the Commissioner] or officer purporting to convey or set forth such approval, sanction, consent, concurrence, declaration, opinion or satisfaction, shall be sufficient evidence thereof.