Why is there :nopm: in some photo file names?
This is not related to AM/PM as the screenshot shows. This issue appears to happen due to Google Hangouts. I have heard from a few Moto G owners that this happens a lot on that device, and can cause issues moving to SD card, however, it really seems to be down to Google Hangouts. 
Here is a mention on Reddit, and on an unrelated thread the same issue crops up. 

Upon reading this issue on Github: 


  google hangouts produce [sic]images of this form image_timestamp.:nopm:.png


There is no easy fix at present, but I will investigate.