I found a way to help reduce the sig size down a couple of KB. The background are all png so what I did was to save the background I had for my sig on my computer, opened paint and loaded the background and resaved it as a jpg file. Went back to the sig editor page and uploaded the new background and unshared the file so it wouldn't show up as a duplicate in the backgrounds already listed. Chose the new background from the files i've uploaded section and let the sig editor do the rest. My sig was still a png but the size went from 23.7 K down to 17.5 K so it can help.
If you feel this is too much you can do what Kirby suggested in reducing the size of your sig or upload a new background of your own. Just make sure it's a jpg when you upload it.
