These are made in Istanbul Zildjian K's. Very desiriable and worth quite a bit more than your average old Zildjian's (but as always, they are only worth what someone is willing to pay). I am not a Turkish K expert, but someone will chime in who is.

I know that there can be "fakes" of this stamp. I'm not sure how prevalent it is, though. I had never heard of a K stamp being faked until I joined this forum.

I'd say you got some pretty collectible and sought after hats, there. We'll see what the others say.