I'm not too fond of the noise around the warglaives, but it's decent otherwise. Also, it's over the file size limit, so you'll want to fix that if you use it.
What does that matter?
jpg has the whole artifacting issue, though, it really depends on what program you use/what quality setting it's at. I use jpg all the time and I never get artifacting.
A maximum quality JPG compressed has variations below the threshold that the human eye can detect, making your choice of format insignificant. The comment by WaeV has no importance to the signature's quality, and therefore little relevance to the topic.