Call it the "Mad Men" effect.

December used to be a slow month for American car sales--that is, until Lexus launched an industry-changing advertising campaign called "December to Remember" in 1998, putting cars on the radar of shoppers looking for Christmas gifts.

Within two years, Lexus was the best-selling luxury brand in the industry, boosted by robust December sales. Mercedes-Benz and BMW followed suit with year-end campaigns that helped revamp formerly slow December sales into one of the busiest periods of the year for the auto industry.

"The idea of giving a car as a Christmas gift went from being an ad agency conceit to a regular occurrence: Plenty of dealers started delivering cars with big red bows on top," Automotive News reported.

December 2014 is projected to be the fourth-best month of the year for car sales even though this December has just four sales weekends instead of five. The auto industry is expected to deliver more than 1.5 million light vehicles this month, according to TrueCar data.

Automakers are increasingly trying to work the holiday shopping angle, incorporating car ad campaigns into the retail sales boost that kicks off with Black Friday.

One thing that red bows can't make up for is bad weather. Last December was something of a disappointment for auto sales, and carmakers blamed the elements. While the month was No. 1 or No. 2 for sales from 2009 to 2012, December 2013 ranked fifth-best month for the year as buyers were discouraged by cold temperatures and storms.

General Motors and Toyota fell short of sales forecasts, reporting December sales that were down year over year; however, both automakers saw a rise in full-year sales, and industry-wide sales hit 15.6 million for 2013, a rise of 7.6 percent compared with the previous year. 

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