Well, since it's your first i wont be to harsh.
Overall it doesn't look appealing.
Some things you might want to change;
The border is way to big and basic a simple black border would have been better
Not liking the lens flare, looks terrible I would advise not to use it in your signatures in the future
Renders look like they've been resized, makes the signature look cheap
Text is way to basic
Try and download some brushes and just mess around making a background
Anyway I suggest you keep trying, I'm no graphics pro myself but I know a fair few techniques which get me by