I'd call this a tag, not a mural. It was on a vacant building, the former UA Plumbers & Steam Fitters Local No. 741 at 2475 E. Water, on December 8... and it was gone the next time I rode by, a few days later.
Of course, what's graffiti to one person might be art to another. I thought of this as I read a couple of recent newspaper articles about tagging in Tucson. (Here's the one from Tucson Weekly.) What if someone reports a piece of "urban art" as graffiti? I'd guess the company that cleans Tucson walls, Graffiti Protective Coatings, has experience with that.