Frequently used proofreading marks:
http://webster.commnet.edu/writing/symbols.htm
Delete:
, 
, or 
Delete a letter: a diagonal line through the letter with the delete mark in the margin
Delete a word: a straight line through the word with the delete mark in the margin
Transpose:
Space needed:
Close up a space:
Delete letters and close up a word:
New paragraph:
Period or full stop:
Semicolon:
or 
Colon:
or 
Insert or superscript:
Insert or subscript:
Insert comma:
Insert apostrophe or single quotation mark:
Insert double quotation marks:
Insert en dash:
, 
, or 
Insert em dash:
, 
, or 
Centered:
, or 
Parenthesis:
Frequently used abbreviations
Let it stand:
Spelling:
Capitals:
Lowercase:
Italics:
Roman typeface:
Bold typeface:
Faulty diction: DICT
Awkwardly expressed or constructed: AWK
Wordy, too verbose: WDY
Wrong word used (e.g. to/too): WW
http://www.ministryofwritinghelps.com/
