Exhibit A, Barton East:

With such a simplistic circle, it's hard to determine what it actually means, but I'm guessing that it might just be a picture of the belly of the UFOs. It would make some sense I guess, since the UFOs emmit a beam from the center of the under-side, and there is a notable smaller circle in the exact center of the circle as a whole. The odd looking parts on the side may represent landing gear of some sorts as well.
Exhibit B, Barton South:

This one, to me, looks like more or less a self impression of one of the UFOs. It's perfect circle, four small circles, and medium sized middle circle hints that to me I guess.
Exhibit C, Great Wall of Gambino:

I'm shooting in the dirt with this one, but the center, not the direct center but just off, looks to be a backwards 50 or backwards and upside-down 20 depending on how you see it. There appears to be a hash-mark on the top and bottom that may signal a 1. I'm guessing that it's a backwards upside-down 20 because the hash-mark would be the sum to subtract from 20, thus making 19. If for instance it was a 50, I would just say that the aliens were cocky. The Appearance of two 50s, in a round about way, to me says "You have only a 50/50 chance of survival." All in all though, it could just be a random piece of alien graffiti.
Exhibit D, Durem Caves North:

Perhaps the creepiest of the circles, this one reminds me of the crop circle from the movie "Signs". Ron Bruise has been saying things that make the Aliens out to be "good", but if we remember how "good" the aliens were in "Signs", I'll be walking around with a fully loaded super-soaker for safety. Also, it may be a hint as how to kill the aliens if there is an attack of some sort, but I'm sure there is some other meanings to this circle.




