Heath Ledger signed dark knight poster in ink?

For christmas I got a why so serious joker poster with a COA verifying that Heath Ledger himself signed the poster in ink. There were comments that Heath didn't exactly sign dark knight merchandise before he died, though I still believe he did. I posted a video about it on youtube at: a href="http://www.youtube.com/watch?v=-SmnDbyWmf0" rel="nofollow"http://www.youtube.com/watch?v=-SmnDbyWm…/a you can either comment on youtube or answer here, please help.