Superstar
Heather K. Phillips' Stamps of Disapproval allow you to comment negatively on a piece of work without having to actually say it. These stamps take the form of ambiguous encouragements like "Good Start" and "Has Potential."

These stamps are perfect for head honchos that don't like coming down upon their employees. I could really see teachers taking a liking to these Stamps of Disapproval. A paper from a thin-skinned student wouldn't be an F, it would just be a "Missed Opportunity".