I've got a 20" Zildjian Crash/Ride (2013 grams) that I'm trying to date. Anecdotally, the previous owner said that it was purchased new by his dad in 1971, and the owner of the music store told his dad it had already been sitting on the shelf for a couple years at that point.
As you can see from the photo, the stamp is extremely light - the Arabic script at the top is almost not there at all, as is the other "Genuine Turkish Cymbals..." text at the bottom.
I've also included some other pix to better show the lathing patterns, bell, and center hole.
Obviously, going by what the previous owner told me, it would most likely be a late 60's/early 70's Zildjian. But maybe some of the real experts here will have a more informed opinion.
thanks in advance,
JohnB