Possible Clues:

• [Wait until you're home to click this!]
• Letters in the subject of a racy email
• 'Avoid watching this at the office,' briefly
• "Office-inappropriate" tag
• 'Watch somewhere else' letters
• Office-inappropriate, for short
• Warning made with H.R. in mind
• Warning initials above an internet link
• (Don't watch this in the office)
• Warning about a racy web pic