They are indicators for identifying your communication status with your friends.
- New!: You have received a new, unread letter from your friend.
- Yellow Dot: Your friend is waiting for your reply.
- Envelope w/ Yellow Arrow: Your friend is sending you a letter.
- Envelope w/ Blue Arrow: You are sending your friend a letter.
- Return arrow w/ Date: You have replied the letter, with the last status update time of the conversation.