Related Clues:

• Tread noisily
• Philatelist's item
• Bring foot down hard
• Washington-to-Boston speedster
• Validation for a letter — tread heavily
• Big name in fast tracks
• Brand of squash
• Passport feature
• Email doesn't require one
• ___ of approval
• Postage buy
• Notary need
• Appropriate star of "The Collector"
• It's often stuck in the corner
• Douglas Hofstadter's '___, Escher, Bach'