The first use of the X brand was on casks of English beer.
It indicated that the contents had been properly aged and had passed government approval after paying a ten-shilling duty, illustrated by the Roman numeral X.
Some brewers added extra Xs to suggest a more potent content, and smut peddlers followed suit.
When something is X-rated by the censors, its naughtiness is enhanced if more Xs are added.
