This is really not bad for a first sig, above average I would say. good job on the lighting, I believe that the lighting came with the background though. Try dowloading some brushes and use them to smudge the render and get it to blend in with your background. Then you can use different brushes for different effects. Good luck, and really good job for your first sig.
This is coming soley from my basic knowledge of design and appearance but... I think that the signature has a very nice fresh and appealing look to it, this being down to the blue and green background (which I almost thought was Valhalla for a second). Sadly, I think the Spartan helmet does ruin the signature a little, as Hayabusa isn't so nice too the eye. As a tip, I'd maybe change the helmet to something that works a little better (e.g. Mark V). The Spartan armour colour does fit in well, nut you could sure experiment with other coloutr to see of they stand out for good or bad reasons too. As for the text, I think that it both fits and looks nice in the context of the sig. Maybe this is because it is of a similar colour to the sky (but on a different coloured part of the image.) Keep the text and the background, but alter the Spartan - its pretty good for a first try. Listen to the G&A guys though, they know what they're talking about ;D
I have to say for a first signature this is pretty good, I second Frag Man, have you had any experience with art before?
well i have use my unique spartan, why is it unique?? well if I play online i never c the same combo armor what I have so that's why it is unique .
No problem with that, I figured this was the case anyway. I'm not saying you have to change it at all, just experiment with designs - it can help with other projects in the future. Like the other guys have said, this is great for a first try.