Really simple, add more depth, lighting is cool,background is boring, could you show me the render you used.
Also no effects in the background except or those little lines.
First sig with Naruto is way too simple. Don't rush art, you'd need to work at least 1 hour on each. What you did with Naruto is just lighten up and use different layer settings, and some editing... Try to add depth to the signatures, here's an example I did about 4 years ago;
Jalis: Freelancer, you're a duck | Sachi: Freelancer, you're a duck | Reanimator: Freelancer, you're a duck
satiknee: Freelancer, you're a duck | Wiggi: Freelancer, you're a duck | Tarlan: Freelancer, you're a duck