Hi, I don't know if this is the correct thread to post this sort of stuff what what size banner should I use for my signature?
An 800x100 banner looks quite nice in my opinion, although you may need to make some adjustments to that.
I usually see 100x800 to 200x800 dimensions. Your current one looks good, but try doubling the height (without distorting, of course ) to make it look nicer.