Its pretty good. Have you tried it with a blurred out background image? Something urban/grey might contrast well with the main characters and fill the blank space the black background has. Almost no one uses dark blacks/greys on the internet anymore, its very 2000. Might be worth experimenting to see if you can find a background that suits it.
Actually the forum sigs seem to be set under a certain size .. 500x300 I believe, and will not let you upload if over it ..
As for the design I will have a rethink and see what I can come up with .. I did like the black at first but now it does look a little off to the foreground.