Anyone old enough to remember the Number Stations broadcasting out of Eastern Europe during the years the Berlin Wall was standing? They were used to communicate with intelligence agents, who needed nothing more than a SW radio to anonymously receive messages.
The Stations used high power short wave transmitters, the broadcast would start with a signature tune often from a worn stretched tape or a Station number ID.
Then a series of numbers would be read out by the announcer or voice synthesizer.
They were always in blocks of 5.

So 2-7-9-0-4 then 9-4-3-6-4 and so on.
Decoding could be by the use of a one-time pad or simply a book.

Where
digits 1 and 2 could be the page number.
digits 3 and 4 could be the line number
digit 5 the position of the word in that line.

The numbers then decoded to reveal the message.

The application of this for Bitcoin could be to code your wallet seed phrase in this way by choosing a book and finding those seed words in the book and converting them to 5 digit numbers.

Then writing down and storing anywhere the series of meaningless 5 digit numbers.

Without knowing from which book and the exact print edition (your key), your seed phrase is reasonably safe.

The cryptographers here will be able to punch holes in this but for good enough protection for regular folk it could work quite well.