I think it may originate with the mil. Heard it used over the years occasionally and even picked it up myself a couple of times. It seems to be a very quick way to check that all is OK if something from the outside looks odd somehow.
If the answer is yes, all well and good and sorry for puzzling you, if the crew have got a problem a quick "no - call you" will be enough to start getting any services that might be handy moving a few seconds earlier than waiting for the mayday.