Possible Clues:

• *Metaphorical boundary that shouldn't be crossed
• What one draws to say 'this far and no farther'?
• Boundary you won't compromise on
• GRcreaseIT
• Metaphorical cutoff point
• Symbol of a challenge
• *Metaphorical boundary
• Metaphorical limit
• Draw a -- (set limits)
• Boundary not to be crossed