the first sig is simple and a bit dull/foggy to look at. Maybe if you brought out the render more by making it brighter or more vivid, it'll look better.

the second sig is a little too long and the middle where you split the two sections is too sudden. Maybe blending it a little more would be better. Also, try sharpening the renders, it gives a good focus.

Last one, again is a little too dull. Try brightening the render more or sharpen it. Then, duplicate the render about two times and set one to screen/color burn (depends on the render) and then the other to overlay/ Soft light (depends on the colors of render as well)