Consent etc., of Commissioner, may be proved by written document under his signature

Whenever under this Act the doing or the committing to do anything or the validity or anything depends upon the consent, approval, declaration, opinion or satisfaction of the Commissioner or of a Deputy Commissioner or any municipal officer, a written document signed by the Commissioner or by such Deputy Commissioner or municipal officer, purporting to convey or set forth his consent, approval, declaration, opinion or satisfaction shall be sufficient evidence of such consent, approval, declaration, opinion or satisfaction.