That would be a late 1950's trademark. About '57 to '59. Have you ever weighed it?
I too would have guessed that one as a 70s due to the thin font on the Zildjian similar to these 2 that I have.
[IMG]http://i802.photobucket.com/albums/yy309/HerronScott/Zildjian%20Cymbals/100_1003.jpg[/IMG]
[IMG]http://i802.photobucket.com/albums/yy309/HerronScott/Zildjian%20Cymbals/100_1059.jpg[/IMG]
Note that the bottom one has a hollow ink logo on it so pretty definitely late 70s through possibly early 80s.
What identifies this one as a 50s versus a 70s?
Thanks!
Scott