nodding dog

noun

a small model of a dog carried as a mascot in a motor vehicle, with a head so mounted that it moves up and down with the motion of the vehicle

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012