A hatrack for your luggage

On a recent flight, I was bemused by a sign on the overhead containers for carry on luggage. The sign advised caution in opening the ‘hatrack’, so that items wouldn’t fall down.

I have never seen this word used before with this meaning. Maybe I have missed out on some new aviation jargon or maybe I have just led a sheltered life.

At first, I thought this was perhaps just a translation error by the airline, so I looked online. This usage is evidently not common, but I did find a couple of useful items:

• A US patent granted to Airbus Operations GmbH in 2013. This is for a ‘modular hatrack for a passenger compartment of an aircraft’. The classification is ‘stowage device for passengers’ personal luggage’ and the diagram does indeed show something looking like the overhead bin on my flight. https://patents.google.com/patent/US20120292445A9/en
  The plane was an Airbus A380-800, so clearly the term ‘hatrack’ came from the manufacturer not from the airline.
• The following exchange on an online forum.
  Question:   I’ve seen the additional emergency exits aft of the wing on the 707-320C and stretched DC-8 models referred to as “hat rack” doors. That strikes me as an odd name, since it seems unlikely that valuable cabin real estate would be taken up by dedicated hat racks, even back in the early ’60s when hats were in fashion.
  What’s the origin of this term? Were there typically seats next to these doors like in any other row, or was it kept clear for easier evacuation?
  Answer: Today’s aircraft have “stow bins”, but way back then, the overhead storage area was just open shelves, and were called “hat racks”. Those “hat rack” emergency exit doors were shorter than the normal entry doors, allowing the hat rack to continue over the top of the door without interruption, hence the name.
  https://www.airliners.net/forum/viewtopic.php?t=754253#1

So that explains the origin of the term. But the word ‘hatrack’ makes no sense today. It isn’t a bin and it isn’t used for hats.