Sometimes when grading tests, teachers will write something like "-2" for a wrong answer for a question worth 2 points. My mom complained that when a student gets a test back graded this way, it focuses on the negatives rather than the positives (correct answers). I think teachers do that so that when calculating the grade, the teacher adds up the deductions and subtracts that from 100. I don't think teachers do that to focus on the negatives, but it is still possible that it could annoy students. How do you feel about grading by writing the deductions for each question?
It's done to make calculating the grade easier. The whole "focus on the negative" is right up there with "might hurt their self-esteem", well to bad. If a test has so many "-2's" on it that it hurts someone's feelings, simple solution: study more and do better! Students look at the big number/letter on the top of the paper.
I agree with NHRef. It simply makes calculating scores easier (which comes in handy when you have a lot of tests to mark and not a lot of time). I don't know why your mom would think this way. Even if she complained, I highly doubt your professor would change his/her marking scheme.