Generally, only classic cars have radiator cap 'mascots' and, probably the most famous of these is those found on Rolls Royces: the 'Spirit of Ecstacy' (known in the USA as the 'Silver Lady' or the 'Flying Lady') and the 'Kneeling Lady' (which made a brief appearance, after its introduction in 1934). The original mascot was designed by Charles Sykes and represented a Spirit of Ecstacy figure, modelled on the features of Eleanor Thornton, secretary and mistress to Lord Montagu of Beaulieu (of the family of great motoring enthusiasts), and this figurine had a finger pressed to its lips; called 'The Whisper', it was symbolic of the secret love of Montagu and Thornton. The more familiar mascot (still modelled on Eleanor Thornton), was introduced in February 1911 and, scaled down, is still to be found on modern Rolls Royces. They were made through Sykes at first and then by the firm of Lejeune, before Rolls Royce eventually took over the manufacture.
In the 1920s and 1930s Jack Buchanan liked to substitute the Bonzo mascot (pictured above, by courtesy of Louis Lejeune), made by Lejeune, which also made the Queen's motor car mascot of St George slaying the dragon and also makes others too. Bonzo was a cartoon dog, created by George Studdy. JB even put them on the above magnificent machine (left click picture to view in its entirety): the last big road car made by Bentley before it was subsumed in Rolls Royce; the 1931 8 litre Bentley. The restored model pictured had actually belonged to JB and the photograph is by courtesy of Michael Daly of the School Garage. Louis Lejeune still make car mascots, including Bonzo.