Nice. How about making the background (i.e. the blank white space that is not the outer ring, text, or inside the "tree bubble") sky blue instead of white? It'd really help set all the other elements off I think. I hate being the "nitpick guy" - it's a nice design, but the white text on white background kind of hurts my eyes.
I also think the tree and bubble could be enlarged a little without detracting from (perhaps even enhancing) the "sign" aspect.