When installed as a git pre-commit hook, this script will prevent a commit from being created if the token '!DNC' is found within the diff.

dnc-hook.sh

#!/bin/sh
exec 1>&2

dnc_count=$(git diff --cached | grep -c '!DNC')

if [ "$dnc_count" != "0" ]
then
  echo "Aborting commit. Found" $dnc_count "!DNC markers"
  exit $dnc_count
fi

exit 0