These are nice, but you need to experiment more to become better. Try different colours (you're only using dark ones at the moment) and different types of brushes. When you get the hang of that you can create your own unique sigs.

Tutorials can really help you out. There are a lot, but this one started me off:

Simple Sig Tutorial - for thous who are new in photoshop...

Good luck, Shadow Bahamut. Looking forward to seeing more from you.

Edit: Also, try using borders, they normally make a sig make more of an impact