Adventure Time's Jeremy Shada will be signing autographs at the Entertainment Earth Booth #2343 at San Diego Comic-Con. Here is an except from Entertainment Earth's press release.
Entertainment Earth is also offering an Adventure Time Themed Convention Exclusive featuring Jake and LSP. You can see pictures of the "Adventure Time Traveling Jake Tin Tote Gift Set" below-
The Tote Set Convention Exclusive is also available to pre-order on Entertainment Earth's website here