Proofreaders' and Editors' symbols
Just like alchemists, astrologers and masons, professional proofreaders and editors used to have an arcane set of special symbols and characters essential to their magic.
Word processing and desktop publishing, together with a much more 'hands on' approach to writing copy, have made them something of an anachronism - a bit like shorthand. But they still have a romantic appeal all of their own.
I am much indebted to the University of Colorado at Boulder for this example of proofreader and editor symbols