1. The background is kinda dark compared to the C4D's you use. And some of these C4D's don't match the flow/theme of it. It's overly contrasted and the text does not fit. Use the rule of thirds. 7/10
2. Great sig. The flow and theme of the sig is good. The C4D and other effects are well placed and looks nice. Using a few other gradients might make the colors balance but overall, nicely done. 9/10
3. For a C4D sig, this is good. The flow is good, the blending isn't as good as the other sigs. The right part of the sig feels out of place and the whole c4d does not match the render. Changing the color/contrast/brightness will probably enhance the image. 6/10
4. Personally, I don't like this sig. The render is a little out of place, maybe a little more to the right. The render itself should have blend with the sig. The bubbles feel out of place, and the flow is in the wrong direction. The C4D in the right does not fit the whole sig. Too dark and different. 6/10
Using more gradient maps will make it better, blending (the render isn't blended in the background), the text isn't that good, other than number 2. You should also add borders.
But overall, very nice works.