Related Clues:

• Playful signal
• What a spy may write in
• Program lines
• Java ingredient?
• Something to crack
• Set of rules
• It's quick, supposedly
• Morse __
• See 21 Across
• Word with bar or zip
• __ of ethics
• Building contractor's study
• Problem for a cracker?
• Morse made one
• One-eyed flirtation