I'm pretty sure the sigs are legit. As other posters have surmised, TM evidently came across a whole pile of these and figured out something to do with them.
When I first saw these coming up on eBay I e-mailed Tim and asked if they were aftermarket re-bindings and what the difference between the 26 edition and the 100 edition. He (I assume it was he; I guess it could have been an associate) e-mailed me back and was very upfront with the nature of the books. Nice friendly e-mail.
I would have bought one for less than $50. I wanted the book to read, the signature is a bonus, and hardbacks are sturdier on the shelf. I would have bought it for what it was--not as a bona fide limited edition.
Thus I made lowball bids on just about every single one of these that came up for auction, or had them on my watch list, just in case one slipped into my hands on the cheap. I estimate I bid or watched on at least 40 copies of the "26 limited" and 150 copies of the "100 issued" version.