There are two types of shields. Those ordered with the car and fitted by the factory and those that are just stick-ons. The stick-ons, you can buy from any accessory shop and have it stuck on the fender, but the with the factory option the shield is "embedded" into a slight recess in the fender.
I think the factory options were only available as of the 360 models. Previous to the 360s the only time the factory installed the "official" shield is on their "special" and limited production models like the F288GTO, the F40, the 328 Competizione and the F50. I am not sure if it was an option item on the last year model F355.
So the shiled is meant to denote a special Ferrari model. But not any more. I have it as a factory option on my 360. And it will be standard on my new Stradale.
