This bookmark was first available at concerts by Molly Lewis and The Doubleclicks during their October 2012 The Ladies of Ragnarok tour. After the tour completed, the bookmark was given out via the standard promo item distribution channels (i.e., with orders from the publisher's online store, at conventions and tournaments, and via Men in Black).
The bookmark name and the tour name are obviously connected, and the three women depicted on the front of the bookmark are almost undoubtedly Molly Lewis (top, with a mostly hidden ukulele), Angela Webber (left, with ukulele), and Aubrey Webber (right, with cello).
In-game Effect - The bookmark may only be used in a game of Munchkin Apocalypse, and it must be played before the 7th Seal is opened. When the 7th Seal is about to be opened, you have two options: (1) destroy the bookmark to prevent the Seal from opening, or (2) keep the (undamaged) bookmark and get a +3 to your item total when the Seal is opened.