[Fedora]

I think the choices are either that the letters are Greek letters, but much more recent than 6000 B.C., or else scratches which happen to resemble Greek letters.

Yes, I'd entertain both of those hypotheses before the hypothesis that it's the Greek alphabet, unless there's additional evidence beyond that potsherd. Perhaps if they ever decipher Linear A it will shed additional light on the prehistory of Greek. Linear A has a character that looks like somewhat that Upsilon/Delta character I mentioned--see for instance left-hand pic, second row, third character from right:

Linear A and Linear B

[SunkenCiv]

bttt, with a link to a related topic:

Macro-Etymology: Paleosigns [writing 20,000 years ago?]
Macro-Etymology Website | prior to May 20, 2005 | the webmasters thereof
Posted on 05/19/2005 11:00:18 PM PDT by SunkenCiv
http://www.freerepublic.com/focus/f-chat/1406892/posts