I think the Hue/Saturation filter would easily work with this render. Since it's gold and white, using the Hue/Saturation would only affect the gold on it. I think.
And if not, well using a Purple/white gradient map and setting it to hue/color (or even maybe on normal) would work well enough.
As far as lowering the opacity of the render is concerned, it would probably look better if the black on the sig is lowered as well... This is decreasing the contrast of the sig, more easily done by brushing in white over the black parts, setting it to soft light, and lowering the opacity of that layer just a bit.
Then what I'd do is increase the contrast of the tag using the Curves filter.
..Being your first tag and all, I would imagine you've no idea what I'm talking about, so Iwouldn't worry about it for now. ;)
Avatar: In memory of ieatwyverns <3
Thank you, Vasco <3