Special Inspector General for Monitoring the ACA Act of 2014 or the SIGMA Act of 2014 - Establishes the Office of the Special Inspector General for Monitoring the Affordable Care Act to conduct, supervise, and coordinate audits and investigations of the implementation and administration of programs and activities established under, and payment system changes made by, the Affordable Care Act (the Patient Protection and Affordable Care Act and the health care provisions of the Health Care and Education Reconciliation Act of 2010). Requires the Special Inspector General to be appointed by the President, with the advice and consent of the Senate.

Requires the Special Inspector General to appoint an Assistant Inspector General for Auditing and an Assistant Inspector General for Investigations.

Places the Special Inspector General under the supervision of the Secretary of Health and Human Services (HHS), but prohibits federal agencies involved in implementing or administering the Affordable Care Act from preventing or prohibiting the Special Inspector General from initiating, carrying out, or completing any audit or investigation.