SIGMMA Act This bill establishes the Office of the Special Inspector General (SIG) for Major Metropolitan Areas. Specifically, the SIG must conduct, supervise, and coordinate audits and investigations of the treatment, handling, and expenditure of amounts appropriated or otherwise made available for use by major cities; and establish, maintain, and oversee such systems, procedures, and controls as the SIG considers appropriate to discharge its duties. Whenever information or assistance requested by the SIG is unreasonably refused or not provided, the SIG shall report the circumstances to the Department of Justice and to the appropriate congressional committees without delay. The SIG shall report on a quarterly basis to such committees and to the Department of Housing and Urban Development.