Why do so many Arizona mountains have letters on them?

There are at least seven mountains in Maricopa County with letters whitewashed on the side. Have you ever wondered why they were put in? Or when? We'll give you one hint: It comes down to more than just community pride.  This week, Valley 101 digs into the history behind the "<Phoenix" sign on Usery Mountain in Mesa, A Mountain in Tempe and S Mountain in Phoenix. Producer Taylor Seely reports alongside Lucy Bentz, a 12-year-old Goodyear student who submitted the question. In this episode you'll hear from: Brennan Basler, a.k.a. Ranger B Arizona State University archivist Rob Spindler  Sunnyslope Historical Society Vice President Pat Wilkinson