In 1990, the Kryptos sculpture was installed at the CIA in Langley, with 4 encrypted messages. One of them, when solved, read as follows:
BETWEEN SUBTLE SHADING AND THE ABSENCE OF LIGHT LIES THE NUANCE OF IQLUSION
And in 1990 it had that intentional misspelling with Q.
Why?
Documents Reveal How the NSA Cracked the Kryptos Sculpture Years Before the CIA
https://www.wired.com/2013/07/nsa-cracked-kryptos-before-cia/