def get_aton(mmsi: str) -> bool:
    """
    Gets the AIS Aids to Navigation (AtoN) status of a given MMSI.

    AIS Aids to Navigation (AtoN):
        AIS used as an aid to navigation uses the format 9192M3I4D5X6X7X8X9
        where the digits 3, 4 and 5 represent the MID and X is any figure
        from 0 to 9. In the United States, these MMSIs are reserved for the
        federal government.
        Src: https://www.navcen.uscg.gov/?pageName=mtmmsi

    :param mmsi: str MMSI as decoded from AIS data.
    :return: bool True if MMSI belongs to an AtoN, otherwise False.
    """
    return str(mmsi)[:2] == "99"