Scott McLemee gently corrects a blogger’s misconception of “-30-,” the apt title of the final episode of The Wire.
McLemee also mentions “TK” and links to the Wikipedia page, called “To Come.” I don’t work in the magazine world, but I did briefly some years ago. Nowadays there’s so little virgin territory left in Wikipedia, I was honestly shocked that an essential and presumably beloved piece of journalism minutiae like “TK” has such an underdeveloped Wikipedia page.
As of yesterday morning, the entirety of the page consisted of two declarative sentences defining the term followed by a long, rather boring quotation from the Chicago Manual of Style in full-on schoolmarm mode disparaging the use. It looked like this:

“To Come” is a printing and journalism reference abbreviated “TK.” It is used to signify additional material will be added at a later date.

The Chicago Style Q&A on manuscript preparation describes it as imprecise, stating, “It’s best to be more straightforward and specific. For example, use bullets or boldface zeros (••• or 000) to stand in for page numbers that cannot be determined until a manuscript is paginated as a book (but see paragraph 2.37 in CMOS). For items like missing figures, describe exactly what’s missing. In electronic environments, you have recourse to comment features—like the syntax of SGML, which allows for descriptive instructions that will not interfere with the final version of a document. Make sure that whatever you do stops the project in its tracks at some point before publication.”

Well! Consider yourself tut-tutted, magazine and newspaper people! And by book people, no less! (I do love the CMS, but their strictures have only questionable utility to magazines, I’d imagine.)
That didn’t sit right with me. I haven’t even seen a “TK” in a professional capacity for several years, but I went and added a reference to the Breeders’ 2002 album Title TK and a paragraph (almost surely to be judged insufficiently NPOV) explaining why “TK” makes a lot more sense at Condé Nast than it does at Random House, where CMS holds sway. It makes sense to me, but it’s just a guess.
There must be a healthy number of magazine and newspaper employees reading this. Surely that Wikipedia page can benefit from your experience and judgment, no?
So by all means emulate Nicholson Baker (a.k.a. “wageless”) and add some information to that entry! “TK” must have an intriguing history! There must be amusing anecdotes! (Most, probably, involving “TK” making its way to the newsstand.) When did it start? Who invented it? Do style guides acknowledge it, or is it more informal? How did “to come” get abbreviated to “TK,” anyway? Is there a procedural justification for doing that? Has anyone ever gotten a “TK” tattoo?
And just think: all the answers are entirely TK.