Back of this sig sucks, and I'm not sure of the pen tool:
Well here are the main issues with it from what I see.
First thing is the background. The render doesn't seem to be a part of it. Like, the render and the background don't match, don't blend...the colors of it all are dull and monotonous too. For the Chibi style, try something simple. Ditch the special effects brushes and keep it to gradients and shapes. You can achieve depth and appeal that matches the style without going over the top. Look at this sig.
Notice how the background is just simple gradients and lines, plus some subtle lens flare work, yet it creates a great illusion of depth and works perfectly here. Something similar to that could work great for the Chibi style for SotW. Also don't erase the edges of the render. Looks like he's fading away which is not really good here.
Next, we have the orange effect. Only thing I can suggest for that is to make it lighter near the center so that it doesn't look so flat, and then also make it skinnier in places, give it some size variances to make it look more realistic/appealing.
Lastly the text, which I can't really suggest what to do for that right now because if you do what I suggested before, it will need a much different text.