This is one of the Artist's Proofs sold by Stan directly to his fans at conventions.
"This is number 12AP of 500 copies of the hardcover edition ... each of which has been individually signed, numbered, and illustrated by Stan Sakai." It has a bound-in limitation page with a 4 inch square where Stan has drawn a full scene with Usagi and a tokage with mountains and clouds in the distance "Eep!"
Volume 8 collects issues 1-6 of the Mirage comic book series Usagi Yojimbo Volume Two, and back-up stories from 7-8, plus a cover gallery. Introduction by William Stout.
From the publisher:
This limited, hardcover collection of Stan Sakai's masterful adaptation of samurai legend includes a dust jacket, printed endpapers, and a signed-and-numbered plate. But the real jewel is the original sketch that Sakai draws in each and every copy! Whether you're an Usagi fan, a fan of Japanese history, or one of the millions of followers of the Teenage Mutant Ninja Turtles (they're in here, too, y'know), you must get this book!