So I picked up this set many months ago, has supposed signatures of each author on the cover.

When I asked about it back then, no one had a copy with signatures on it and Strato said he had the designers copy and it too had no signature

However when I look on the internetz I see references here and there to 'signed' copies. One was on nobleknight but with no picture. RPGnet mentioned signatures as well

I suppose my question is this...has anyone heard of or seen a copy with signatures?

I have Richard Snider's copy and included in the box was a 4 page letter explaining his perspective on the production of Adventures in Fantasy and his relationship with Dave Arneson. One of the interesting details is that Snider was paid a nickel a box to sign his name to all of the box tops.

aia wrote in Adventures in Fantasy Arneson/Snider Excalibre Games:My copy is signed and every copy i spotted on ebay was signed... Actully i dont recall any copy without signature...

I didn't see any signed copies on ebay. Unless I'm not looking in the right spot. My copy is signed on the front of the box

Yes, that is where they signed them, on the front of the box.

I have had 4 copies of this set, 3 were signed and 1 was not.  Most of the ones I remember seeing while hunting small press stuff were signed.