^It's the lower edge of the Starfleet arrowhead emblem. Although, yeah, it does suggest a hilltop or something.
It seems very dark and ominous for ST, but maybe the idea is that, as with the Star Wars
OT, the second film is like the second act in a three-act story, where complications set in and the situation becomes worse, with the third film/act being the resolution that makes things better again. Maybe the third film will be Star Trek Into Light