First question: Are you using photoshop?
Now for the signature...it's not bad for someone just starting out, you're experimenting still and you're not going to have a great piece at your level of knowledge. I would lose the text and try to stay away from text in signatures unless you feel it is absolutely vital but in that case I would suggest sticking to solid colors rather than throwing it on overlay.
Focals like what you have here require a different approach, one that I usually do not use. Not really sure how to correct you on how to make this better simply because I usually use images from a front view usually of people. One thing I can say that you can fix is the blurriness of the turn table.
One final thing I would like to add is to not add things just because you like them, add them because they look good. I know that goes against personality but if you plan on taking a step forward in the area of graphic arts the first thing they will always tell you is to consider your audience. While you can keep similarities among your pieces to develop an artistic personality I would suggest not adding things like the radiation sign in your pieces.
Other than those few minor details it's not bad for someone just starting out. I'd like to see more from you.