I would render each person separate of the BG (including volcano) maybe do them in pairs to make it easier. Drop the sig height, kinda even everyone out so as to fit the new sig height and redo txt, add border, and customize BG.
Dude, make your sig's smaller. Don't embed youtube videos, it's just fucking annoying.
Anyways I think that many changes are needed.
One thing the gradient in your text is very strong, try and make a lighter gradient inside with the color's not varying from too much eg. Red to a lighter Red.
You should also get an idea of resizing and adding borders.
I prefer the 350 X 150 Pixels size, but people have other ideas on that.
Just make sure it doesn't go too big because it tends to annoy lots of people.
I also recommend looking at Chronologix's beginner signature tutorial that teaches you about basic brushing and what not.
I'm no expert, but I have improved a lot by trolling through the Signature Tutorials section. You'll improve, and make sure to post future work to get some critique and what you should do to improve your work.