Apologies for the delay in CC for this.
The following is intended as constructive criticism please do not take this harshly.
Considering your extremely difficult stock and render choice, the outcome is impressive, and I commend you even more considering you're "not a designer". This is impressive. With this in mind, I thought I would provide some CC to help you in the future.
Your placement is what made this most difficult for you, you should consider moving it to the right a little, so that your right side of the signature isn't so empty.
This is a touchy, and sensitive subject, but I feel that your colouring needs a little work. I feel that darkening the edges and adding spotlights would work wonders for your theme, and really help to highlight the "runic" and mystic theme that you were going for. Here's an example:
(this is just a quick and rough example)
As the above shows, darkening the edges helps to focus ones eyes on the render and the mystic text behind. This helps to set the mood and makes the signature seem less "empty". I have also duplicated the text behind the render and added a colour dodge to make it pop out a little more. Again, to help set the mood.
I disagree with @OMGhixD's suggestion of blurring, it takes too much away. Darkening (like above) would suffice in my opinion.
I do however, agree with the lighting aspect, which is my next point.
As the above colouring edit shows, the left (as you look at it) is darker than the right. So we need to reflect this with our lighting:
Personally, I feel your lighting would be best like so:
So, use a soft brush with white opacity in this sort of area.
I used two layers, one near the render, and one near the top. Play around with opacity to achieve desired effect:
I also darkened the bottom to achieve something like this:
(Again, this is just a quick and rough example)
I hope that this CC goes towards helping you, and that you continue to develop your GFX. I see a lot of potential and I hope you continue it. I look forward to seeing more!
disclaimer: These are suggestions intended to help the OP and should not be taken in an offensive manner. The suggestions are subjective and not definitive. Please take with a pinch of salt and use to experiment on your design(s). Enjoy!