Sharing here for those who might appreciate a good primer on the subject. For me it began with the shape of the sheaths and progressed from there.
I can now see how these can lead to another field of study unto itself.
I believe this knife is carried by every man in certain countries / sects so it is far from rare. Probably hundreds of millions out there and every family has a bunch. I am sure there is still a market for quality makers or antique blades but it would be difficult to find an expert on this in the US. And since most of the examples in the US were probably bought as souvenirs finding a truely rare and valuable example here is remote. Still cool though.