m. c. de marco: To invent new life and new civilizations...


Mark Liberman at Language Log meets thirty for the first time, and restricts it too narrowly to newspapers although the earliest citations don’t mention them:

1895 Funk’s Standard Dict., Thirty..among printers and telegraphers, the last sheet, word, or line of copy or of a despatch; the last; the end. 1929 Amer. Speech IV. 290 ‘30’ or ‘Thirty’ indicates the end of a shift or of the day’s work, and has come to mean, also, death.

The XXX theory of thirty seems the most likely, for its similarity to ###.