From The Heretic Knowledge Vault
A tiny bit of art work by Poe that isn't part of the story but features one or more story characters or episodes, given as a small gift to those who donate and keep this great story afloat. It differs from filler art in two regards. First, it doesn't appear on a particular day as a substitute for a story installment, but rather is updated monthly on a regular basis. Second, it isn't freely available to everybody. A bookmark is one of the perks for donating money to keep the story and the associated business (Caffeine Angel Studios) alive and well, and comes in hard copy via snail-mail after you donate.
Most of the main characters have appeared in bookmarks at one time or another. At present (January 2008) the bookmark features Ellis getting harassed by Rape-kun, which is one of the running gags in the Fun with Familiars omake strips.
Information on donating, as well as a thumbnail of the current month's wallpaper, appears here. You can also click the "Donations" item on this page's sidebar.