Wow! How can you tell? Would it be considered an A or a K?Thanks!
As Zenstat pointed out, Avedis Zildjian's are "A's". A. Zildjians have always be made in the US since the early part of the 20th century when part of the family moved from Turkey. K. Zildjians were made in Turkey until the late '70s or around 1980, I believe. The Avedis Zildjian company bought it out and moved production to North America. When people are refering to vintage 'K's' they usually mean those Zildjians made in Turkey.
Both A and K Zildjian changed the metal stamps a number of times over the years. Sometimes the changes were subtle, sometimes not so subtle. Drumaholic has devised a timeline for the manufacture of both A's and K's based on these stamps, the cymbal lathing and hammering characteristics, and other idiosyncracies such as hole size, bell shape, etc. That timeline is the standard for determining the age of cymbals from different periods. Your stamp is a typical '60s stamp. I hope this helps.