OK, I’m stretching a little here, since it’s not a Serenity item. But this 18″x24″ print of the cover of Buffy #1 is signed by Joss and Jo Chen, who did the Kaylee cover for the Serenity comics, and Buffy was wearing a Serenity t-shirt in the first issue of her new comic, and and and…
OK, I just thought it was cool. If the price is too high you can also get the print signed by just Jo Chen.