I earlier proposed something similar to the "#PARENT" idea, but I'd like to warn against it as used here: just using to creat the link is bad. We can already create links to parent articles, and we _should_ do so with plain English sentences that establish context. Remember the "establish context" rule? The article "Generalisimo Francisco Franco is Still Dead" shouldn't just have a hidden tag that puts a link to SNL in the title bar rather than the article; it should begin with a clear English sentence, "Late-night variety show [[Saturday Night Live]] contained a news parody..." Sentences. Good.
My idea was "#CONTEXT", which was used to do the other thing that subpages are useful for, and for which I currently use them, and that's to simplify cross-linking among pages within a subject area. See the Poker pages, for example; but the same thing could be done with "Law", "Medicine", "Mathematics", etc. My idea was that if a page contained a "#CONTEXT Law" tag, then any link in that page like [[bar]] would, when the page was saved, search first for a page "Bar (Law)", and only then "Bar". Likewise, under "#CONTEXT Chemistry", [[deposition]] would look for "Deposition (Chemistry)" and then "Deposition" (hopefully a disambiguating page), but never "Depostion (Law)".