I have written a paper (only internally marked) and I have a title:
"GCR2: A Riddle, Wrapped in a Mystery, Inside an Enigma".
This was initially a Winston Churchill quote about Russia (after the colon anyway). However, it seems silly to reference it directly in the title and I have been looking around on the web and cannot find how to reference something that only appears in the title.
Any guidance or links to websites will be very helpful (although I couldn't find any!)
No-one would expect a reference in the title. There are a few alternatives you can consider.
The simple one would be to add "(Winston Churchill)" after the quote in the title.
A better option in my opinion, is to start the introduction with the same quote built into an explanatory sentence and then add the reference there. After all, the quote must have a significant meaning for your work, otherwise it would not form the title. I am not sure what the "GCR2" stands for but in general one should avoid abbreviations in the title.
A third possibility is to rewrite the title to something more explicit. you can have the quote as the main title followed by a subtitle that explains the significance. Different field have different ways of handling such titles so I cannot say what would be suitable for you. The title should draw attention to your work and make readers decide whether the work is worth reading. For me it has no meaning and although I am in a different field, I think that is a sign that the construct is not optimal.
Leave the title as you suggest,
GCR2: A Riddle, Wrapped in a Mystery, Inside an Enigma
without any citations or quotation marks, or any mention to Churchill or any of it. In the introduction of the paper, however, make sure to mention where appropriate the quote, and to give the appropriate reference(s) to it.
In particular, do not try to add footnotes, or references to the title. Any of it would result in turning a clever choice of title into something very confusing, which may further lead to unintentional mistakes when others try to reference your paper.
(Truth be told, I imagine --hope-- a referee would ask you to change the title if you tried to include footnotes or the like.)
If you are worried that you are not giving due credit to Churchill (hehe) or somesuch, don't. Your introduction will hopefully clarify all of it.
In fact, if your title were something like "To be or not to be. Of proteins and men", where what you quote or reference is essentially universally known, I would suggest not to bother explaining it anywhere, as it could be perceived as you suggesting your readers would not understand it otherwise, and they in turn may react negatively to such a suggestion.
I think that phrase is so trite that it almost doesn't need a citation.
All that said, if you want to avoid the ugly of an endnote in the title, you could use the phrase in the first para or so of the intro (not the abstract) and then put an endnote citation on that first usage. This also has the benefit of cluing in the unwashed towards the beginning of your paper (and making the smarty pants pat themselves on the back).
For example: "In 1952, Winston Churchill penned the famous quote "blabla" to describe the secretive Soviet Union.(endnote number1) In recent years, GCR2 has drawn the interest, and frustration, of researchers trying to understand how it [does whatever it does]. This review will describe the major recent findings and remaining questions for this critical protein [or whatever it is]."
In some other case, I could even imagine just adding the citation number superscript to the title.
I advise not to weight a title down with (Winston Churchill). Titles should be strong and brief. Don't weigh a title down with a parenthetical. That's worse than the ugly superscript number.
While I love the quote, you could also consider to kill it in the title. There is a point of view in science writing (and all writing) that you should find whatever you did that you think is cute and kill it. Note, I'm not endorsing this...I like a little "juice". But it is an option. However, it does work very well for the title of an oral talk (where a little "tease" is helpful).
This is not unheard of, though it's fairly uncommon.
My favorite example, which may give you some insights on how others have handled their desire to use a reference for a title (especially if you can access the published version):
One Ring to Rule Them All ... and in the Darkness Bind Them?
The authors quickly explain why the plain meaning of the two references are relevant (they were studying "black rings", and there was "one" that basically governed things; and black holes and bound states were discussed, hence the second part), and there's a footnote in the acknowledgments/funding disavowing any association with the Tolkien estate.
