Possible Clues:

• Abbr. for someone who has just a first and last name
• Letters used in the absence of a letter
• Abbr. for a person with only one given name
• Application form abbr
• Name placeholder in govt. records
• Abbr. for John Doe, perhaps
• Abbr. for someone with just a first and last name
• It indicates a void in some govt. records
• Application placeholder
• Application abbreviation