Image host site

I remember that sig being transparent at the top. The weird thing is that the image is in a '.jpg' format, which doesn't allow any transparency.

if the problem would be the image host, I'd recommend https://imgur.com/ and http://tinypic.com/
I doubt that will fix anything though.

There are few image hosting services that converts the uploaded format into .jpg even if the prior image was a png/gif format. And that´s why your signature lost it´s transparency, if you still have the original file of that signature I would suggest you to upload it on www.imageshack.us (I use this one quite a lot actually) While the servers may be a bit slow but imo it is sufficient enough for a signature.