One of the first large projects I was assigned when I started working with The Fun Pimps was to completely redo the achievement icons. There was a lot of fun creative thinking to be had about recognizable symbols (and fun references) I could make. Some of the referenced icons involve recognizable objects from the game, such as the vehicles for travel distance.
Also, given that the icons were created in Illustrator (using Vector, in other words), it was easy to repurpose them for the Xbox Game Pass release as well.