Possible Clues:

• Letters denoting "so you know"
• Interoffice letters
• "I thought this'd be helpful" acronym
• 'By the way,' on a memo
• "Thought you should know," on a memo
• Corkboard posting letters
• Memo-header notation
• Email forwarder's intro
• Sticky-note initialism
• 'I thought this'd be helpful' acronym