If a cause is important enough or offer promising enough to create a chain-mail message for, it would probably have a companion website. If the message doesn't provide a link to some resource to verify the information, it is probably false. Keep in mind, however, that getting free web space and e-mail addresses is incredibly easy. E-mail petitions are useless. E-petitions are just too easy to fake.
Electronic signatures are too easily forged and too difficult to verify.
Hoax warnings and petitions are frequently used by spammers and cyberstalkers to obtain a list of possible targets. Just look at the header of one of these multiply forwarded messages and see all the addresses there. Take a petition where well-meaning people attach their names and home towns, and you may be giving a cyberstalker a powerful weapon. Never attach personal information to a message that may end up in a stranger's hands. Believe it or not, the general goal of the press is still to provide unbiased reports of the facts, and that doesn't include rousing emotions.