Folding seems clear; you might fold a card to fit in an envelope, or a pocket. But you’re not supposed crease these cards; that would jam the machine. Punch cards aren’t to be used in your ways, for your purposes, but for those of the company that issued them. “Spindle” is the word that most confuses people today. Spindling is an old filing system; a clerk would have a spindle, an upright spike on his or her desk, and would impale each piece of paper on it as he or she finished with it. When the spindle was full, you’d run a piece of string through the holes, tie up the bundle, and ship it off to the archives. (The custom still survives in some restaurants; the cashier spindles the bills as customers pay.) But you shouldn’t spindle the cards: they are part of someone else’s system of paperwork, not your own; they demand special attention.
“Mutilate” is a lot stronger than the other words. It expresses an angry intention on the part of the mutilator, or, from the viewpoint of the punch card user, a fear; people might take out their frustrations on their punch cards…. (Indeed, punch cards were mutilated: users could buy machines advertised to “recondition mutilated punch cards.”) Why would people mutilate punch cards? Punch cards were the interface between the public and the billing system. Metaphorically, they were where the person meshed with the corporate world. —Steven Lubar (Originally published in 1991.) — (Steven Lubar’s home page)
“Do not fold, spindle or mutilate” is right up there with “Abort, Retry, Fail” of the DOS era, “CTRL + ALT + DEL” of Windows, and the following dialogue from Marlowe’s Doctor Faustus:
Faust. Come on, Mephistophilis, what shall we do?
Meph. Nay, I know not. We shall be curs?d with bell, book, and candle.
Faust. How! bell, book, and candle,?candle, book, and bell,
Forward and backward to curse Faustus to hell!