As long as cars have been for sales, alluring models have been used to entice buyers. Margery Krevsky's new book "Sirens of Chrome: The Enduring Allure of Auto Show Models
" looks at the history of both kinds of auto models. Some of them are literal "human hood ornaments," like this Marion Morgan Dancer showing off a 1927 Packard 343 Series Eight. Others may not climb on the hood -- but still play the role of ornament to the cars they are helping to sell.