by Merriam-Webster Online Chicago Manual of Style Online
Unfortunately, the former Merriam Webster Online link to this information no longer works. No worries. There are plenty of other places to find proofreading marks. These are commonly used when editing any type of document in a law office. If you are not familiar with them, I suggest that you print the list for easy reference.
Another excellent website that provides an abundant amount of information, including proofreading marks, grammar and punctuation, dictionaries, and other reference resources is RefDesk.com (https://www.refdesk.com).
If you decide that neither of these are your cup of tea, just search “proofreader marks” with your favorite search engine. -CCE