Shield Master Achievement
Collect 20 Master Shield pickups.
Shield pickups are much like Hazard pickups, "QA" will alert you of a new pickup when one is available. Unlike the Hazard pickups you will find the shields in a small pod on the ground.
If you find an area where a shield is ready to pick up close to a checkpoint, you can pick it up, die and re-collect it over and over. Doing so will allow you to earn the achievement without having to worry about picking up shields as you progress.