The Winter Soldier. they will kill off the Steve Rodger/Chris Evans Captain America in a few years and Bucky Barnes/Sebastian Stan (now the winter soldier) will take his place. it happened in the comics
If you’re quite familiar with the symbol below, it could be the Deathly Hallows symbol from Harry Potter. If you know that, then I’m assuming you also know that a deer has so much value for a couple of characters in the story.