:o A GFX artist, I haven't seen one besides me in a long time.
Hmm, to be quite honest, I can't really give you much CnC since it looks like you've followed BakaArts's tutorial videos. It's been a really long time since I've watched them, so I don't know how much of it is true to the original videos, but the style definitely looks familiar and regardless, I won't fault you for it. I do like how the third sig came out, it has a nice finish and the color scheme works well.
One criticism: The lighting on the first sig is kind of weird. The teal doesn't match very well with the render and doesn't look right because it's on top of the shadows of the render. What you can do to fix this is move around some of those light sources so that it matches better with the render's lighting and color pick the lighter part of the render.