The Memo is a function in Virtue's Last Reward. It allows the player to write notes relating to any puzzles or story elements that may be important, such as passwords. It is a representation of Sigma's brain and the information in it.
There are two pages to the memo function. Information written on these pages carries over from timeline to timeline.
The Memo function can be opened from the Novel screen, Puzzle screen, and the Archives screen.
As Sigma makes more jumps through timelines, the information on the Memo function becomes slightly distorted and with enough jumps, can possibly become illegible. This is due to the Memo function acting as Sigma's brain in some respects. As Sigma loses some of his memories with each jump, anything written in the memo will get distorted. This is hinted at with the words "brain memory" written on the memo.