Origin of "Period" and "Full Stop" as Interjections

Solution 1:

The OED on stop deals at meaning number 18 with full stop. 18a concerns the punctuation mark. But 18b deals with full stop meaning a conclusion. But I do not see any indication of its use as an emphatic indication that no further discussion/consideration will be possible or tolerated - in the sense of We are done, full stop. See below:

b. transf. and fig. in various senses, e.g. a complete halt, check, stoppage, or termination; an entire nonplus. Also = period n. 11b.

1628 J. Earle Micro-cosmogr. xxxviii. sig. G6v, He is the Period of young Gentlemen, or their full stop, for when hee meets with them they can go no farther.

1655 Ornitho-logie 30 She therefore that hath not the modesty to dye the Relict of one man, will charge through the whole Army of Husbands, if occasion were offered, before her love will meet with a full stoppe thereof.

1711 E. Budgell Spectator No. 77. ⁋1 After we had walked some time, I made a full stop with my Face towards the West.

1719 W. Wood Surv. Trade (ed. 2) 233 All Persons depending on the Turkey Trade, were at a full Stop for many Months.

1735 Swift Gulliver Introd. Let., in Wks. III. iii, Seeing a full Stop put to all Abuses and Corruptions, at least in this little Island.

1798 J. Ferriar Eng. Historians 237 The story thus comes unexpectedly to a full stop.

1815 Scott Guy Mannering III. viii. 149 He drew up his reins..and made a full stop.

1861 ‘G. Eliot’ Let. 6 Oct. (1954) III. 456 There is a point of disgust..which one feels must make a full stop, and call for a Finis in friendship.

1923 P. Selver tr. K. Capek R.U.R. i. 10 It was in the year 1920 that old Rossum the great physiologist, who was then quite a young scientist, betook himself to this distant island for the purpose of studying the ocean fauna, full stop.

1962 Observer 1 July 8/5 The controversy has been between those who say yes, full stop, and those who say yes, but…

1971 ‘R. Amberley’ Ordinary Accident x. 92 Once he sends for a lawyer then that will be full stop.

Solution 2:

The original high dot and low dot were apparently invented by Aristophanes' Byzantine namesake; forgotten for a few centuries; and revived a few years after the invention of the printing press.

Singularly enough, the invention of the modern term full stop is sometimes attributed to Shakespeare:

SALANIO
I would she were as lying a gossip in that as ever knapped ginger or made her neighbours believe she wept for the death of a third husband. But it is true, without any slips of prolixity or crossing the plain highway of talk, that the good Antonio, the honest Antonio,--O that I had a title good enough to keep his name company!--

SALARINO
Come, the full stop.

(from The Merchant of Venice)

It's either him or "origin unknown," and we're all too fond of good old Will not to give him the benefit of the doubt.

The full stop thing is not actually the dot at the end of the sentence: it is the mental gap between two thoughts, the syntactic equivalent of "over" in the radio communications voice procedure.

It is unknown why the Americans began to favor "period" over "full stop" in the beginning of the 20th Century. Apparently, it has nothing at all to do with telegraphy.

Thus logically it makes more sense to use "full stop!" rather than "period!" as an interjection.

Now if you use Ngram Viewer and make the year 1600 the starting date, you will see that after multiple reprints of Merchant which would account for the peak of 1650, the frequency of use rises towards the middle of the 18th Century, which coincides with the initial boom of journalism and its favorite venue, i.e. the newspaper. Needless to say, journalists and printers back then socialized a lot more than they do now, for obvious reasons.

It is safe to assume, then, that the printer's slang became part of the journalist's slang, and that's probably how the term entered entered common speech in England and elsewhere.