Extended validation certificates are identity certificates issued to a legal entity. This means that anything signed by that certificate is "guaranteed" to come from the entity instead of just from the domain name.
Since phishing emails are a big deal and (at least in my mind) appear to be growing in prevalence, why don't companies sign emails using these certificates (and include the signature as an attachment)?
The trust infrastructure is already (mostly) in place and the verification could be handled fairly transparently by email clients using the OS or browser certificate store.
I imagine that this could render many of the "ENTER YOU BANKING CREDENTIALS IN 24 HOURS OR ACCOUNT WILL BE DELETE" emails and other, better crafted phishing emails, largely useless to the phishers.