If you remove the scrolling matrix code in the background, and keep all the other effects (text, video), the sig will be a lot smaller.
Note my sig - it has a decent lengthed animation. Yet it's tiny 
This is because (I'm not sure, but from what I've noticed), GIF filesizes depend on how much is animated. If only one portion of the picture is animated, the frame only needs to be changed for that pixelated area... if its the whole frame, it takes a whole framesize of memory, which makes it big :0