There were only 6 copies of Signature made. There would have been more or Write made, and are probably in some attic in the house of the former editor. When it is found, I would guess a value on it of about $3000-$4000 (assuming that only one copy is found. If the entire print run was boxed and never sold, we will all be able to afford a copy), but there are really only a handfull of people that would pay that. I would not pay it. As much as I would love to have one, If I found one in a thrift shop, I would almost certainly sell it. I can think of only maybe 5 or 6 people that are obsessive enough to HAVE to have that and have the means to pay for it.
I would rather have Signature, any day...
Best,Bill
p.s. To make my point above; Anyone remember when "Peace Amongst The Ants" sold for $300 a copy on abe and there was only one copy available? Fogel valued it at $175.00. That was before a massive cache of mint copies showed up in Anaheim, CA. I assume that they were from the publishers stash and that very few copies ever made it out at the time of publication. They probably sat in a box for almost 40 years and then the publisher decided to unload them. I have 10-15 copies of that here and know others that bought 20 or more at $24.95 each.