Arthur Conan Doyle, approached by a popular magazine for a contribution, thought up Sherlock Holmes and proposed a story called The Sign of the Six. Posterity knows that the story was numerically diminished, and published as The Sign of the Four.
As signs go, a 6 looks like it's in curly retreat whereas a 4 seems like it's making a protruding statement. It's the dramatic difference between Zorro and his Bangladeshi counterpart ëJorro': in three intersecting strokes of the whip the Latino cowboy establishes his authority and its promise of vengeful justice. Jorro, however, has some difficulty getting the whip to hook into a 'J'.
The word chhakka which is, beyond dispute, the name of the number 6 in 'Indian' (Hindustani), has a more graphic provenance.
But first its definition. It's a noun used exclusively to describe males. There is no such thing as a chhakki. The stigma of the six does not apply to women. It describes the ineffectual and the incompetent, the wretch who is ludicrously unequal to a task.
And there lies the key to the metaphor. The 6 of chhakka doesn't refer, as ë69' does in European languages, to the pictorial shape and suggestiveness of the numerals. The 6 of chhakka belongs to the altogether different grammar of the position on the dial of the numerals of a clock.
The chhakka, the six, the lowest numeral on the circular dial, mourned by the drooping hour hand, becomes the symbol of impotence. The chhakka is the drooper, he who can't raise the flag of competent manhood, an impotent fool.
The word passes into the language even as the circular dial is abolished by the digital clock, all numbers clicking away. No springs, no gears, no round clock-face, no high noon, no chhakka.