“30” or “Thirty” (no more; the end)
Wikipedia: -30-
-30- has been traditionally used by journalists in North America to indicate the end of a story or article that is submitted for editing and typesetting. It is commonly employed when writing on deadline and sending bits of the story at a time, via telegraphy, teletype, electronic transmission, or paper copy, as a necessary way to indicate the end of the article. It is also found at the end of press releases.
The origin of the term is unknown. One theory is that the journalistic employment of -30- originated from the number’s use during the American Civil War era in the 92 Code of telegraphic shorthand, where it signified the end of a transmission and that it found further favor when it was included in the Phillips Code of abbreviations and short markings for common use that was developed by the Associated Press wire service. Telegraph operators familiar with numeric wire signals such as the 92 Code used these railroad codes to provide logistics instructions and train orders, and they adapted them to notate an article’s priority or confirm its transmission and receipt. This metadata would occasionally appear in print when typesetters included the codes in newspapers,[1] especially the code for “No more – the end”, which was presented as “-30-” on a typewriter.
Wikipedia: Wire signal
A wire signal is a brevity code used by telegraphers to save time and cost when sending long messages. The best-known code was the 92 Code adopted by Western Union in 1859. The code was designed to reduce bandwidth consumption over telegraph lines, thus speeding transmissions by utilizing a numerical code system for frequently used phrases.
Google Books
Instructions for the Running of Trains, &c., on the Erie Railway,
To take effect January 1, 1862
New York, NY: Press of the Erie Railway Company
1862
Pg. 64:
ABBREVIATIONS.
NUMERALS.
(...)
30. Finis.
Google Books
Instructions for the Running of Trains, &c., on the Atlantic & Great Western Railroad,
To take effect January 1, 1863
Cleveland, OH: A. S. Sanford, Printer
1863
Pg. 58:
ABBREVIATIONS.
NUMERALS.
(...)
30. Finis.
Google Books
Wood’s Plan of Telegraphic Instruction
Arranged by the Professors and Tutors of the “Morse’s Telegraphic Institute”
Syracuse, NY: Morse’s “Telegraphic Institute” Association
1864
Pg. 69 (Telegraphic Numerals):
30—Finis.
Google Books
3 October 1868, The Telegrapher, “Correspondence,” pg. 46, col. 2:
You made me say that we were expected to remain on duty until three o’clock A. M., whereas I think I said “30” (good night) on night report. (...) OWL.
Google Books
Instructions for the Running of Trains, Etc., on the Atlantic & Great Western Railroad,
To take effect July 1, 1872
Meadville, PA: Republican Steam Printing House
1872
Pg. 75:
ABBREVIATIONS.
NUMERALS.
(...)
30. Finis.