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

(dbus-event-bus-name EVENT)

Return the bus name the event is coming from.
The result is either a Lisp symbol, `:system' or `:session', or a
string denoting the bus address. 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.