Yeah, at some point i started wondering how many people
- ride US airplanes
- understand spoken English
- have never used a seatbelt
I have to think it’s a very small number.
I’ve always got a kick out of the phrase, as well as the song London Underground . Which was why when my gf went to London (with a friend from work; they did a week of pubs and cemeteries) she brought me back the hat.
I interviewed a guy who used to be a manager at a popular clothing chain found in many malls. He put it down as one of his job duties.
Took me a minute.
Actually it was virtually unknown in the UK throughout the 20th century - the signs were printed during the war, but never widely distributed. In about 2000 someone found one and publicized it
“To the pure, all things are pure.”
I know a maverick CFO who was brought to task by his board for reporting the company’s finances in an unconventional manner.
Apropos of nothing and completely off-topic, ever since seeing The In-Laws (the hilarious 1979 film with Peter Falk and Alan Arkin, not to be confused with several others of the same name) I can no longer hear about airline safety demos without chuckling.
At one point in the film, Falk’s character and his lunatic brother-in-law are on a small private jet crewed entirely by Chinese who speak no English. Despite it being a private plane, James Hong, playing a flight attendant, proceeds to do a hilarious safety demo entirely in Mandarin, with gesticulations to aid comprehension. Near the end he demonstrates inflating a life jacket and then, clasping his hands together like a swimmer on a diving board, demonstrates how to dive out of the plane. He then pantomimes a swimming motion. Satisfied with a job well done, he smugly settles down to read a magazine. According to comments in our movie thread, the scene was challenging to film because Falk couldn’t restrain his laughter! 
Interesting; I am sure my parents (both of whom were born after the war) told me about the phrase well before 2000. Although they (and consequently I) have/had a talent for retaining fairly useless facts. So when it started popping up on postcards/t shirts etc (we’d probably call it a meme online now?), I knew exactly where it came from.
Sometimes there’s a teenager taking their first unaccompanied plane ride. I was seatmates with one once. Nice kid.
Who has never used a seatbelt?!
In fairness, aircraft seatbelts typically have a different unlatching mechanism than the ones you usually find in cars. That’s probably the only point to the seatbelt part of the demo.
I can’t remember when I first heard the phrase, but it was fairly recently.
It made me think of a line in The Silence of the Lambs, both the movie and the book.
Right before Lector escapes, the he tells the guard bringing his dinner to “mind the drawings”. I.e., don’t disturb Lector’s drawings on the table. Which forced the guard to put the dinner on the floor to move the drawings, and then reach down to pick up the dinner. Which enabled Lector to handcuff the guard to the cell and escape.
“Ready when you are Sgt. Pembry”.
He’s probably used a seatbelt. But I could see someone, even a repeat traveler, going “What do I need this for!? Are we going to crash into a cloud!?” Emphasizing that seatbelts should remain fastened throughout the flight isn’t the worst policy.
But I might need to get out my seat quickly if there’s a snake.
They’re like the ones in old cars. I remember those kind of seat belts in cars in the 70s.
Ahahahahah! I came in to post that very thing. I find that skit hilarious. My wife does not.
Back to the OP - never mind “mind the gap”, WTF is a tannoy?
A public address loudspeaker. The (UK) brand became a generic term.
ETA: apparently the company still exists, making (home/studio) speakers.