If a completion mark is earned in Hard mode without first earning it in Normal mode, the game will count both the normal mark and the Hard mode mark as unlocked. If objectives are completed in Hard mode, the completion marks are outlined in red. If objectives are completed in Normal mode, the completion marks are solid black. As you complete these objectives, the post-it note on the character select screen fills up with Completion Marks. Completion marks are earned by completing specific objectives in The Binding of Isaac: Rebirth.