Lets start at 1
Sig 1 - This looks like a really good signature, I feel like it goes all very well, the render, the background, and the colours. Although it does not have much depth or flow, it looks like a very good abstract background, and a creative render, Although some of the blending could use some work (looks like you could have just taken the render and turned it on like.. colour blend) I see that both the top right and bottom left corners are pointed out, that would look good if you had a sense of flow towards these two points, maybe trying to achieve that would complete this signature.
Sig 2 - The only have a few complaints about this signature, the red i think needs to be a bit darker.

that render reminded me of that sig i made 3 years ago, its very dark, i personally think that worked well, but its up to you haha.
Sig 3 - This is very simple, but works very well, I think the text is too big and attracts your attention too much.
Sig 4 - There is little to no blending in the signature, It seems as if you stuck two signatures on each other, it could use some blending work, you could copy the render a few times to the left and right and smudge it a lot, and then have the earth fading through or something like that.
Sig 5 - This is a good start, the render could use some blending though. i like the use of the render on the right side, faded in the background.
Sig 6 - This looks good, I just think the bullet damage maybe should follow the angle of the gun, and the background I don't think suites the render.
Sig 7 - There is real no sense of blending in this signature, it would make for a good pop-out signature, but the render needs to be blended a bit more to the background, and it doesn't seem like a great render. The faded render in the background could work well if you make the render blend a bit.
Over all you did a very good job for a beginner!