#2 GMV, it portrays the theme of summer very well. I don't know how much time was put into it, but compared to all the other sigs, this one gives you the strongest impression of summer. The sky, the sunflower, the dusty feel of it all gives this feeling. Since this competition is about how well the sig complements the theme, and not how much technical skill or effort put in, #2 GMV.
#1- Has the technical merit there, however, something just doesn't match up to me. I'm thinking it might be the background. It's nicely done, however, the lighting on the right suggests that it's sunny. The lighting background to the left suggests that it's dusk or dawn. This for me seems to break the flow of the sig. If appropriate changes made to either side (ie color of lighting of the light on the right side or the color of the sky on the right) it would greatly help the sig and make it better than #2 IMHO.
#3- Nice and smart. But the text kinda kills the entire thing. Would've better if the text was left out and something else replaced there (a background, window of outside? maybe? dunno.)
#4- Um, I'm not sure if that's the ocean or the sky. The random lens flare is probably supposed to be the sun, but doesn't work for me.