This tech tip from Sean McBride of ITS (if you need any help using this feature, please call the helpdesk at x7293):
We have recently deployed a newly added security feature within the Google Apps Email system. It specifically designed for email that has a “spoofed” or fraudulent email from: address that may state it has been sent from a user within the @augustana.edu domain. This tactic is normally employed by spammers and the like to attempt to circumvent normal spam blocking sweeps. Now any email that has originated from our augustana.edu Google Apps email system is digitally signed with an electronic water mark and users can now check their own email if they have doubts as to the validity of the item.
Below is a screen shot with the newly added signed by security field highlighted. By hovering over the “down arrow / triangle” after the list of recipients in an open email a “Show details” popup will appear, clicking it will bring up the mini window pictured in the screen shot below. The user can then see whether this email was digitally signed by our Google Apps system.