Hi Gang,
Have a vintage Zildjian Swish with 6 Rivets in immaculate condition. I would love to sell this for sale or trade for an Istanbul Agop (Trash hit, Traditional, or Special Edition, etc).
I found out that the stamp likely dates the Swish to the 1950s (Trans Stamp). Not only does the Swish not have the hollow logo on the bottom, as was used in the 1970s, but the stamp matches with those far preceding said period (distinguished by a deep even press stamp). In addition, the logo appears to match those shown on a few of the A. Zildjian Stamp timeline histories:
http://www.hidehitters.com/cymbals/Z.../timeline.html
Here is a poor attempt at a sound file. I hope this helps (sorry about the sound quality, as the room is completely empty and without soundproofing).