dbus-event-member-name is a compiled Lisp function in `dbus.el'.

(dbus-event-member-name EVENT)

Return the member name the event is coming from.
It is either a signal name or a method name. The result is a
string. EVENT is a D-Bus event, see `dbus-check-event'. This
function raises a `dbus-error' signal in case the event is not
well formed.