Lots of reprints of that one around right? Or are they reissues? It was discussed at some point...
Most of these you see frequently offered on ebay are FAKE. The guy who made them initially sold them as originals, now he offers them as 'reprint/reissue'.
The paper stock of the fakes is different, but the easiest way to spot the difference on a digital image are small white spots in bottom. They slightly vary in size, but are present on all originals I have handled. On the fakes, the bottom section is spotless black. Heritage has images of several originals online, and if you know what to look for, the spots are easy to see. This poster was issued unfolded, so there's a number of rolled originals out there.
Over the last 20 years, I have probably handled more copies of this poster than anybody else. I was always rare, but in recent years it been really, really tough to find.
Helmut