NYC artist Victor Ving and his photographer girlfriend, Lisa Beggs, are traveling the country painting murals inspired by vintage "Greetings From..." postcards. They get help from local artists such as Rock Martinez who painted the letter "C". The images are: T-Univ. of AZ; U-Saguaro cacti; C-Dia de los Muertos (Day of the Dead); S-Hotel Congress & John Dillinger; O-San Xavier del Bac & Man in the Maze; N-Sonoran hot dog. Photographed on Feb. 22, 2017.
The Arizona Daily Star article Muralists paint a Tucson postcard and the Tucson News Now story 'Greetings Tour' makes stop in Tucson to paint new mural have more information.
Update (August 24, 2017): Here's a March 17th closeup of the bottom right corner: