This mural is on the north side of a building, along the west side of 6th Avenue, just north of Speedway. Since traffic is one-way northbound, you'll pass this beautiful mural before you can see it... and, once you do, it may catch you by surprise!
When I opened a satellite view from Google Maps and clicked in front of the mural location, it showed the address as 1125 N. 6th Avenue, and the latitude/longitude were 32.236419,-110.968997. (It's probably easiest to just park nearby and look around.)
The mural is dated 2009, and I took these pictures on May 11, 2011. The photos below seem to be artists' signatures. If you know, please leave a comment below or send me some email.