This reminds me of an infamous chemistry exam that no longer existed at my college by the time I got there but had passed into the student lore. For each question, you would first mark your answer (multiple choice, 4 or 5 choices), and then mark a confidence option. These were "high confidence" (5 points if right, -3 if wrong), "low confidence" (3 points if right, 0 if wrong), and "I don't know, give me a point" (1 point regardless of what answer is marked).

This exam was not popular with the students.