Possible Clues:

• Muse about wild animal losing tail
• Award talked about on "Mad Men"
• Annual advertising award
• Painting turned up after century, source of inspiration for historian
• Sister of Calliope, Erato, Euterpe, Melpomene, Polyhymnia, Terpsichore, Thalia and Urania
• Advertiser of the Year award, e.g
• Mythical figure often pictured holding a book
• Muse about painting being returned
• Award won by Don Draper on 'Mad Men'
• Ad writer's muse?