Even though I'm not an "expert", I can certainly attest to Glocks having unique firing pin/striker markings. Every once in a while, I manage to pick up brass at the range that isn't mine. I can immediately tell which brass isn't mine, as it seems that 95% or more of the people around here have Glocks!
The Glock - fired case is immediately obvious: the firing pin "dimple" has a drag mark on one side, with a rectangular shaped "scuff" or impression on the primer, surrounding the dimple. Of course, many, if not most, of these also have bulged cases at the case web! I'm not kidding: I could prove it, if I had a digital camera. I've bags of Glock-marked cases in 9x19mm, .40 S&W, 10mm, .45 Auto in my closet, and at least 90% of them all have the bulged cases - even the 9's.
Most of the cases are Winchester-Western (Winchester "White Box" ammo), Federal, Starline, and PMC, for some reason. There are Speer ones, too - but few, if any, of these have the bulges.
I can also immediately tell my own cases, also. All of my primers have "primer flow" back into the firing pin hole, which gives it a raised, "crater-like" apperance. This happens no matter who the manufacturer is of the ammo/case/primer, or how hard the primers. I don't know if this phenomenon is unique to Taurus PT-92 series pistols (and Beretta's), other makers, or just my particular pistol, but I've only seen cases from one other pistol that resembles mine, and the "crater" was not nearly as deep or raised (pistol unkown, brass was also "picked up" with mine).
Now, I don't like Glocks. I fully admit it. They just don't fit my hand, no matter what the model or caliber. I also don't like their track record, or the stories of their "indifference" - whether this is endemic to the company as a whole, or just Gaston himself. Sure, they're popular, made in just about any size you'd want, and stuff if widely available for them - But I'll never, EVER, buy one. Ever. Not even if it was given to me. But that's me.
I just wish that people who buy Glocks - and other makes, as well - would do the research and homework with an objective eye that they do with other consumer purchases. Would you buy a car that might blow up around you if you just happened to put 87 octane gas in it instead of 93 octane? Or a DVD player that self-destructed when you put in a movie by Paramount instead of one by Universal? Or a toaster that caught fire on raisin bread instead of white? No, you wouldn't - so why do people still insist on buying more Glocks? Especially without insisting on a redesign, or a recall? It's crazy...
Ok, rant mode off...
Anyway, in my experience, it's certainly possible to look at a case and be 90%+ sure of what pistol make it came from. Now, that's not 100%, of course - I'm sure other tests must be made to be 100% sure - but it's close.
BTW: I don't EVER reload range pick-ups, especially ones from Glocks. They go into a bag, sorted by caliber, to be traded in or sold. Now, if they're scrapped and melted into new brass, or reloaded by someone else, I can't control after they're out of my hands. This is exactly why I never buy someone else's reloads - personal or commercial - and never buy ammo of unknown origin, especially at a gun show. My life, and the lives of those around me, is worth a hell of a lot more than the few bucks I'd would've saved on that crap.
ONLY USE NEW BRASS, OR BRASS WHO'S HISTORY YOU HAVE PERSONALLY OBSERVED THROUGHOUT IT'S LIFE. Reload the same cases as many times as you like (or deem safe), as long as you KNOW it's history since new, and what it's been through. The life you save may be your own!