“TK” meaning “to come” is another one. “More TK” in particular is now a blogger affectation but it seems to have been a way to communicate to an editor that a story was so far incomplete, within the text of a submission, without the editor assuming the words “to come” were part of the story. And elsewhere it indicates a placeholder that needs a fact to be confirmed and filled in before publication.

it seems to have been a way to communicate to an editor that a story was so far incomplete

When the story was complete, the notification varied from newspaper to newspaper, but very often they followed the AP's convention of writing "-30-" which I have always believed was something the AP print wire actually (and surprisingly) adopted from the broadcast side, because broadcast stories were ideally 30 seconds long.