With Patch 10.1, Blizzard is adding a new reward for hitting Legend in Rated Solo Shuffle: a Pennant toy.
According to datamining, this reward is also being retroactively added to Season 1, meaning players that achieve Legend: Dragonflight Season 1 will also receive a Crimson Legend’s Pennant when Patch 10.1 launches. This, however, hasn’t been confirmed by Blizzard in any capacity, so it might not happen.