both of those sigs are rather flat. and very basic.. no depth, source of lighting, very dark...
It would help i think if you were to look at your lighting points on the renders in which you are using, and start from there. Also add more detail to the foreground, and background. because currenty right now, it looks like you took a black background, put a white line through the niddle, or the blue through the middle, and then used the smudge tool, did an artistic render, sharpened it, and then added text to it