his name
    `message_keyword` : str
        If not None (the default), the handler function will receive
        the `dbus.lowlevel.SignalMessage` as a keyword argument with
        this name.
    `arg...` : unicode or UTF-8 str
        If there are additional keyword parameters of the form
        ``arg``\ *n*, match only signals where the *n*\ th argument
        is the value given for that keyword parameter. As of this time
        only string arguments can be matched (in particular,
        object paths and signatures can't).
)