message in a bottle

noun2

1. •
   A message written on a scrap of paper, rolled up and put in an empty bottle and set adrift on the ocean; traditionally, a method used by castaways to advertise their distress to the outside world.

   • I'll send an SOS to the world / I hope that someone gets my / Message in a bottle — 1979
2. •
   (figurative) An analogous message sent off into the world or universe without knowledge of who the recipient will be: plaques on craft launched into outer space, interstellar radio messages, stationary time capsules, balloon mail, and so on.

   • 'Cause you could be the one that I love, oh, oh, oh / I could be the one that you dream of, of, of / A message in a bottle is all I can do-oo / Standin' here, hopin' it gets to you — 2021