Related Clues:

• Postal token
• That comes to a sticky end underfoot
• Let 'er get to put 'er foot down
• Put your foot down on 6 across
• Put your foot down on correspondence
• Show petulance
• Purchase that's canceled
• Really put one's foot down
• Symbol of approval
• Slam one's foot down
• One sticks to one's post
• Tread heavily (on an envelope?)
• Philatelist's item
• Bring foot down hard
• Validation for a letter — tread heavily