Marks

 are an addition that increases the amount of points that can be acquired for the respective kind and increases gain. It can be found under the "Stamp" tab of the Notebook.

Using a Mark will remove it from your Notebook.

Obtaining

 * A mark can be obtained from the Gacha.
 * A mark can be obtained from the Lost Memories event, which occurs when you left the game and uninstall it for an amount of time. You can go back and play and do some missions to obtain loads of marks and a character unlock card