The MHRA Style Guide Online
A Handbook for Authors and Editors • Third Edition
From Chapter 10, 'Footnotes and Endnotes'
10.3 Position and Numbering
Wherever possible, a note reference number should be placed at the end of a sentence. Notes should be marked in the typescript by superior (superscript) numbers, with no punctuation (full stops, parentheses, etc.), in sequence throughout an article or chapter. A note reference number should follow any punctuation (including a parenthesis) except a dash, which it should precede. It should appear at the end of a quotation, not following the author’s name if that precedes the quotation.
A note reference number in the text should never be repeated to refer to the same note; if the same material has to be referred to again, a parenthetical reference in the text — ‘(see note 1 above)’ — is the best method, though a new note using those words is a possible alternative.
Do not attach a note number to a heading or subheading; an asterisk may, however, be used to indicate a general note to an entire chapter. Nor should a note number (or, indeed, an asterisk) be attached to the title of an article; a note attached to the first or last sentence, or an unnumbered note preceding the numbered ones, is preferable.