There's an old magic trick out there that's been in the public domain for so long, its origins seem to have been lost.
In the classic version of the trick, a card is chosen, and a mysterious person is called. Somehow, this person is able to name the correct card, despite not even being in the same room, or even the same state or country!
Magicians know this trick as The Wizard, as most of them learned the version by that name from the book, Scarne on Card Tricks. You can read that particular trick for free online (page 42, page 43).
As with many tricks, the presentations grow and change over the years. Some magicians also know this same trick as The Phantom or some other equally mystic name. When Scam School taught this routine (YouTube link), their figure of choice was a secret member of a government conspiracy:
If you think about it, any bit of data which can be identified by two simple pieces of information, in a manner similar to grid coordinates, can be coded in a similar fashion. It's quite obvious that playing cards can be broken down into 2 bits of information, their value (Ace through King) and their suit (clubs, hearts, spades, diamonds). What if the data to be coded didn't have 2 such obvious factors? If we could manage that, this routine could be even more deceptive!
Max Maven developed a version called Remote Pager in which a word is chosen from the following old letter
Impossible, but true! A demonstration of intuition, custom tailored for you by Mister Zulu. Cnoose any word in the paragraph of at least four letters. After you choose a word, contact me by phone. Believe it or not, I'll announce the word you are thinking of! Imagine tne surprise ~ but be on guard: I presume my demonstration is going to haunt you...How would you even begin to code the chosen word? Even being familiar with the above methods, the particular coding isn't easy to work out here.
If you can't figure it out for yourself, Word Ways magazine wrote up Remote Pager here, complete with the explanation. As with all of Max Maven's routines, the approach is subtle and ingenious.
Play around with this routine, which is even more portable now thanks to smartphones. If you have any fun stories of performing this, I'd love to hear about them in the comments!