This mailbox has a roadrunner flag on it and what looks to me like a stylized frog underneath:
I took the photo on November 13, 2011. (That was around the time I got the idea for this blog. I've been collecting photos since then.)
By the way, Tucson has lots of plain-looking mailboxes with a flag in the shape of an animal, a saguaro, etc. I won't show all of them.