From the artist on Tumblr:
 
i wasnt a huge fan of the canon cutie marks for the cmc so i redesigned them a bit! i still don’t reeeeeally like the idea of them sharing a color scheme/symbol, but i tried to re-use elements of their canon cutie marks to suit their original talents a bit more while keeping with “same cutie mark/cmc icon” theme
 
applebloom’s is meant to look both vaguely like a flower and a potion/perfume bottle, sweetie bell’s is a bell, and scootaloo’s is probably the most common interpretation with just a wing, a wheel, and a lightning bolt. the wing and lightning bolt are in her canon cutie mark, and i just added the wheel because it made more sense with her name than … the other one haha.
 
i also kept their adult designs pretty similar to their filly ones, because tbh i don’t like it when people change their looks to be super different from their original designs. short haired scootaloo always!