If one day, you really make something of yourself, and then a student will get that same textbook and see your signature, your name in it.
What will they be able to tell about you by your handwriting, or the color pen you chose?
Will they know who you are? Will they recognize your name? What will come up if they decide to Google your name? What kind of life will you have lived?
Will they be inspired by you? Ashamed? Disappointed? Motivated? Impressed?
What kind of effect will signing your name in that textbook have on another student’s life?