I got an answer! Which is speculation, but an interesting one.pic.twitter.com/ansgLPQLgc
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This 1884 source says to "push the carriage back". But I don't see what model they were using. https://books.google.com/books?id=vQtQAAAAYAAJ&dq=remington%20typewriter%20hold%20space&pg=PA211#v=onepage&q=remington%20typewriter%20hold%20space&f=false …
Aha! 1877 publication describes combining S and I for dollar, using the spacebar. https://books.google.com/books?id=ca05AQAAMAAJ&dq=remington%20typewriter%20exclamation%20period&pg=PA2677#v=onepage&q=remington%20typewriter%20exclamation%20period&f=false …
It shows a list of available characters but does not show the tricolon.
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