Here are some of the abbreviations that I commonly use when grading student work:
#--add a space
VPR--vague pronoun reference
VT--signals an inappropriate shift in verb tense
CS--comma splice
SP--spelling error
AWK--awkward word choice or phrase
WC--questionable word choice; word may not be appropriate in the given context
AGR--lack of subject/verb agreement; lack of pronoun/antecedent agreement
SS--sentence structure needs work
DM--dangling modifier
MM--misplaced modifier
ll'ism--lack of parallel structure
P--punctuation error
Dic--faulty or inappropriate diction
Trans--transition missing