The Sign of the Sibyl is now available in e-book and paperback formats on Amazon (including Amazon UK and other European subsidiaries). 
The process of publication is a little more drawn-out than one might anticipate from outside, and a few practical details still need to be ironed out. In particular, it will take another week or so before you can look inside the print book, but, in the meantime, the sample chapter remains available, as does the look-inside function for the e-book.
Safekeeping will take a little bit longer, but it should be up in September as anticipated.