Possible Clues:

• Convention IDs
• Luggage attachments
• Spooner's domesticated shrews aren't wild horses with labels
• They identify broken horses, according to Spooner
• They hold people's handles
• Stickers that might replace introductions
• Many of them say "Hello!"
• Handouts at sign-in desks
• Means of identifying different types of horses including tips for Musselburgh, Epsom, Taunton, Ascot
• A spy chief enters agent's new forms of ID