Perform the following actions to unlock Shields in Driver Details.

Concepts Shield - Beat all Concepts Challenges on any difficulty
Generations Shield - Beat all Generations Challenges on any difficulty
GT Shield - Beat all GT Challenges on any difficulty
Mustangs Shield - Beat all Mustangs Challenges on any difficulty
SVT Shield - Beat all SVT Challenges on any difficulty
Thunderbirds Shield - Beat all Thunderbirds Challenges on any difficulty
Trucks Shield - Beat all Trucks Challenges on any difficulty