The prophets from the Halo shooter game are an example of a floating hologram on a figure's forehead. The emblems on your characters look like they are attached. A shadow or light reflecting under the emblem will help separate the emblem from the forehead.
Do you have any sketches you can post?
http://halo.wikia.com/wiki/Prophet_of_TruthAlmost everything in the picture is given an equal amount of space which makes it seem flat. Maybe more attention to space by making the picture more flat and graphic or more 3D with a feeling of actual space.