Let's say you are moving to the new league from Silver 3 to Gold 1. In this case you will receive a special Gold insignia!
You will earn special insignia everytime you are moving up to the next league: Silver 1, Gold 5, Platinum.

Progression inside the league will reward you with the case, which contains fragments of the weapon.

Does amount of fragments increase with the league?
Yes! The higher your league the more fragments you will receive!