From Aussievintagedrumuser
The S symbol above the Giant Beat logo probably means it's NOT a Giant Beat but a Stambul as there's NO letters/symbols above both "Giant Beat" & "Paiste" fonts&logos the latter actually stamped onto the cymbal the earlier inked on i've had quiet a few/lot of early 60s Giant Beats&wish i never sold them! after 14 15" hats&18" crash/rides&24" ride!.
...but not yet strongly evidence based from what I can see. I'm not an expert on all Paiste stamps, but I've done a bit of work on Paiste 602 stamps, and Avedis Zildjian stamps so I'm somewhat familiar with what details to look at. And I'm not seeing merit to the Stambul theory based on what I see so far.
The Giant Beat trademark stamp is quite distinct from any of the Stambul ones I've seen. The Giant Beat trademark stamp is at 3 o'clock (unusual for Paiste) but the Stambul trademark(s) are in the more common 12 o'clock position. The lathing on the cymbal is fine Giant Beat lathing not Stambul lathing (which has larger tonal grooves more like 602s) as seen here on this 13" Stambul:
[img]http://black.net.nz/cym2015/13-514-stambul.png[/img]
The direction in which the lathing passes through the stamp (vertically on Giant Beats) tells you the stamp is a 3 o'clock rather than 12 o'clock. For stamps at 12 o'clock the lathing passes horizontally through the stamp, as it does on the 13" Stambul I've shown above.
Check out the wiki entries on Stambuls, you don't need to take my word for it:
http://www.paiste-only.com/paistewiki/index.php?title=Stambul
The S above the Giant Beat trademark wasn't necessarily put there by Paiste, although Paiste do sometimes produce variants of cymbal lines such as the Arbiter 602s, or this unusual 602 with the extra stuff above the 602 stamp including a 5 pointed star. But none of the extras take away from this being a Formula 602:
[img]http://black.net.nz/cym2015/Dynastar-602.png[/img]
Yes, in your case, the font of the S is possibly similar to the S in the Stambul die stamp, but I'd really need a much better photo to be sure. I've got a couple of different examples of Stambul S shapes (it varies). And the Stambul S isn't the same shape as the Stambul 65 stamp either.
http://www.paiste-only.com/paistewiki/index.php?title=Image:Stambul_65_Stamp.jpg
which is also at 12 o'clock not 3 o'clock. And based on the pic you have of that Stambul 65, you an also see that a Stambul 65 has the lathing with the larger tonal grooves.
Of course I might just not be familiar enough with some rare Stambul stamps I have not seen before. But I'd like a bit more evidence before I throw out the idea that yours is just a Giant Beat with an additional S on there. I see the expected stamp in the expected location and the expected lathing for a Giant Beat.