This is fairly simple and straight forward.
Start a thread with the title of your character.
Within that thread post "I would like to reserve [INSERT CHARACTER'S NAME]"
The thread then becomes your very own Notepad. Where you can jot down notes about your character or significant in character changes made during an RP.
Perhaps you are going to be away for a while? Post it there!
You can post anything you want in YOUR character thread!