Here’s a quick writing tip used by the professionals…
When you are writing and there’s something you need to come back and insert later, like a reference, figure number, table etc, you probably leave a note for yourself as a reminder.
Do you have a consistent system for these “notes to self”? Or do you do it a different way every time?
When you have a tight deadline, it is easy to miss (insert figure here) or (find reference on X) when you scan through your document in a hurry.
So it’s better to have a system where you can’t possibly miss them!
TK is wisely used in journalism and printing as a placeholder for missing material, standing for “to come“.
The reason TK is used rather than TC is that it is an unusal letter combination (try to think of any words in English containing “tk”… there are a few, but not many), so if you do a CTRL-F search in your document for “tk” you will find every instance easily.
You could use XXX or any other letter combination that doesn’t appear in the rest of the text. If you are doing a thesis on pocketknives, for example, XXX is probably a better one to use.
Whatever you use, be consistent, and you will avoid submitting a thesis with an embarrasing (insert example here).