Other
Spelling police.com: Proofreaders' Marks
A general list of marks and symbols a proofreader may use in correcting and editing a piece of written work.
Other
Eei Communictions: Standard Proofreading Marks
This resource presents a table of standard proofreading marks. The table indicates whether the marks would be used in the margin or in the text, but does not give examples of the marks in use.