A hood/bonnet ornament, or radiator cap, or car mascot is a specially crafted model of something which symbolizes a car company like a badge, located on the front center portion of the hood

Hood (vehicle)

The hood or bonnet is the hinged cover over the engine of motor vehicles that allows access to the engine compartment for maintenance and repair. In British terminology, hood refers to a fabric cover over the passenger compartment of the car...

. It has been used as an adornment since almost the inception of automobile

Automobile

An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

s.
In the early years, automobiles had their radiator

Radiator (engine cooling)

Radiators are used for cooling internal combustion engines, mainly in automobiles but also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating plant or any similar use of such an engine....

 caps outside of the hood and on top of the grille

Grille

A grille or grill is an opening of several slits side by side in a wall or metal sheet or other barrier, usually to let air or water enter and/or leave but keep larger objects including people and animals in or out.-Spelling:In the United States, "grille" is used to differentiate the automotive...

 which also served as an indicator of the temperature of the engine's coolant fluid.