Related Clues:

• SASE, e.g.
• Letters on letters
• Dict. shelfmate
• Something in an env.
• Abbr. on 14-Across
• Abbr. on a business letter
• Memo header
• Ltr. insert
• Abbr. at the top of a memo
• Stamped return env., e.g.
• Abbr. on an order
• Bus. envelope notation
• Env. abbreviation
• Memo heading
• Collier's, for one: Abbr.