A symbol doesn’t have to be an event. Objects, locations, settings, characters; all of these and more can work as this type of device. A symbol is simply one concept or idea that is used to relate to or represent another. They are often used to reinforce characterisation and plot, adding additional meaning to what’s happening in the story.
Video-games have a unique relationship with symbols. In a way, every game is full of them, because games are designed to use one concept to represent another. The health bar on your screen doesn’t actually function as your character’s well-being, but it represents their health. There are also narrative symbols, like the helmet lying abandoned on the ground in Halo: Reach, which symbolises the devastating losses and deaths which occur in the game.