Medal of Honor: Frontline

As the trophy says, this can only be achieved in Level 13 On Track. Towards the end of the level, as you exit the room where there was a hanging crate that exploded, DON'T jump on the train just yet or the level will end. Immediately look straight up and to your right when you exit the room, this event triggers immediately the moment you pass through the doors. You should be able to spot the UFO in the sky, going in that direction. The trophy should unlock at this point. Here's a video to help you.