The official design for the main Nebula Siren, by *ryancody
-- one of many of a type of strange alien life-forms in our upcoming comic, FAILSAFE
The sirens usually appear humanoid in shape. They are deep black, and appear to be part of a nebula of colorful clouds intermixed with black and multi-colored gasses. The only white in their design is their outline, their eyes and mouth, and a starfield pattern.
The main Nebula Siren in the story, and a number of others, appear as sultry feminine forms.