If your profile visit setting is Normal, your name will be left automatically for each profile you visit. If you switch your setting to Quiet, your name will not be left automatically. You'll have the option to leave your name by clicking Tell [your friend] you visited near the top of their profile. After you've left your name, it will appear in your friend's profile visits, along with the date you visited.
You can adjust your setting at any time. For desktop users, click My Classmates® in the top portion of any page. (For mobile users, click , you may have to expand to make your selection). Select Privacy. Next to Visit profiles anonymously, select the option you prefer (Normal or Quiet).