There are two kinds of physical books of Asteroids, one is autographed. "Asteroids" physical book: one is the first two episodes, which are still being published. The other book, divided into five, is out of print, but it can be bought in the second-hand book market.

Signature means autograph. To sign is to write one's own name, especially to express agreement, recognition, responsibility or obligation. Signature has more interpretations, such as digital signature, art, signature and so on. Signature is a kind of signature, because the signature is used the most, so the signature is often mistaken for signature.