I just came across 〆 for the first time, used as an abbreviation of 締・閉:
Then found the vertical equivalent of 々 --> 〻
Of course we’re all familiar with the prolonged sound mark ー in kana, which belongs to this category.
So I went investigating and found the following:
ゝ Repetition of last hiragana. More common in names: さゝき => ささき
ヽ Repetition of last katakana. トヽロ => トトロ
ゞ Repetition of last hiragana but adding dakuten.
ヾ Repetition of last katakana but adding dakuten.
〱 Repeat last kana.
〲 Repeat last kana + dakuten
〵Repetition of last word.
〵Repetition of last word + dakuten.
Edit: further info for anyone curious:
Can anyone confirm if they’re used all that often?
In print at all, or mostly handwriting?