I'm probably only one, but i found a very strange bug on the Diablo sig.
If i play a video on Windows Media Player in the background, and have this window on top of it, there are few pixels in the sig that are transparent and i can see the video through them...Strange...
Now for the Ontopic comments:
I'm really liking the the Ryu sig, maybe just use bit a smaller font to make it look more sophisticated.
The Diablo sig has a purple glow on the top left corner, its not bad. Maybe just change the colour a little less purple and more like red? And then there is the sharpness that Synth mentioned already, especially on the right side of the sig...
For now i cant really think of anything else, they really cant get much better.