Mexico 1893 8 Reales, KM~377.10, AM?

I have been going through some of my coins and I came across this coin. I identified it years ago and it has just been in a pot with many others, but I am interested to know what some of the letters in the catalogue mean.  Scrolling down the list of dates, next to the year are the letters Mo AM. I know the Mo is the mint, but what is the AM? I am hoping the coin is real, I've had it over 10 years, and it weighs 26.93g. It is non magnetic, so the marks are not rust.

They are the Assayers' initials. There were many, across the years. Krause lists them in detail, a sample - 

when we get to Mexico City mint, however,

So we will likely never know who A.M. was. 

Thank you for that.