Manuscript Preparation, Copyediting, and Proofreading
Q. I have looked online, in your book, in the dictionary, and in numerous textbooks but cannot find the answer to this question: when correcting proof, what mark should a proofreader use to indicate that a word or words need to be underlined?
A. Since underlining rarely appears in published texts, this is not a common mark for proofreaders, but you can underline the text and write “underline” or “u.s.” (for “underscore”) in the margin with a circle around it. (If you underline the word without the clarification, the typesetters will set it in italics.)