〆

Found this info while trying to determine whether there's a kanji stem for the restrictive -kiri suffix; bracketed transliterations added:

〆 is an unofficial character for しめ [shime]. しめきり [shimekiri](due date) can be written as either 〆切 or 締め切り. I recommend the latter.

I think "〆切" is probably a typo for "〆切り"; still investigating. However, the string "二人切り" does appear in various Google results, so I suppose that's the proper kanji-maximized version of futari-kiri ("just the two of us", "us two alone" etc.) after all?

More nonstandard pseudo-kana/kanji and specialized punctuation listed here.

...and finally, an explanation for something that's occasionally puzzled me:

[The quotation-mark lookalike ゛ (濁点, dakuten)] is occasionally used on vowels to indicate a shocked or strangled articulation..