Mercedes was probably the one who remained using the hood ornament for longer. It was stolen very often, so they had to come up with a detachable design.
I guess the ornaments are in decline because they wouldn't pass the DOT, as they can be dangerous to the pedestrian in case of accident. The Mercedes star folds to the back and can be detached, but most of the people never put it on as it is a pain in the back. I remember there was an aftermarket grill in which the ornament could be raised and hidden electrically, at the touch of a button.
The one that I've always liked for what it means to me as an spaniard is the Hispano-Suiza ornament.

When I was in Frisco, walking and sightseeing, after visiting the Colt tower and walking down to the financial district I saw a Rolls-Royce, parked on the street!! It was almost dusk, never ever had I been so close to one, so...................... I touched it and continued my stroll.