This green mailbox isn't especially interesting by itself, but it shows a way that some people avoid going outside (in this case, by the green mesh gate) to get the mail. Though I didn't actually check it, boxes like this usually have a second door inside the wall.
I snapped the photo on June 12th. You can also see it — with a lot of other “flat” art — on the Tucson Murals Project blog. (It's in today's April 18 entry.)