Enhanced Photographs of Mexico pencil signed Walter something

Any idea of the photographer for this 9 1/2” x 7 1/4” photo. It is signed but cannot make out last name. I have four different photos all signed and with Mexico the theme
TIA, Bryan

 

Can you post more signatures?

 

Walter something-pkam, I think. The DF is Federal District, so somewhere in the vicinity of Mexico City. It was an artist hangout in the 20s and 30s, so that makes perfect sense.

 

I see Walter (Middle Initial -- maybe M?) Jokam

 

Walter L..pkan. I see a "pkan" at the end. But look at how he writes teh x for Mexico. It looks like an s. If that k wasn't there I'd say Walter Lipman