A manual for writers of research papers, theses, and dissertations, 7th edition - Kate L. Turabian 2007

Multiple dashes
Spelling
Part III. Style 20 spelling

When you quote from a mutilated or illegible text or represent an obscenity, indicate a missing word or missing letters with a 2-em dash (formed with two consecutive em dashes, or four hyphens). For a missing word, leave a space on either side of the dash; for missing letters, leave no space between the dash and the existing part of the word.

The vessel left the——of July.

H——h? [Hirsch?]

It was a d——shame.

A 3-em dash (formed with three consecutive em dashes, or six hyphens) is used in bibliographies and reference lists to represent the repeated name of an author or editor (see 16.2.2 and 18.2.1).