If you do not have any markings then how you know what is the type of cymbal? Crash? Ride? Thin Crash? Heavy Ride?To me the weight is the most important factor on vintage cymbals, especially Zildjian.
I agree. Since old cymbals probably have no ink marking as to show what they were sold as, or what the manufacturer's intentions were for that pie, grams are the only way to identify it. However, ideal weight is subjective. Grams do tell about about a cymbal. A 20" pie weighing in around 1800 grams will have very different qualities than one of the same size weighing 2800 grams. What is ideal? It depends on you want it to do for you.
Incidentally, yes, the ones around 1800 are very much in demand, especially if it is a vintage K. Not a lot of those floating around, as Zildjian cymbals always seemed to be on the "chunky" size when it came to weight. Heh. I don't think much has changed with them through the years.