Recently a client has required a designed signature for their emails. Whilst in Outlook there’s no issue applying these and there was only a few accounts, the big bugbear was their iPad and iPhones. Pasting the signature into the iphone got haphazard results at best and the most people would recommend would be to “shake” to undo the auto formatting . Even then embedded images were lost requiring we moved them to be externally hosted. The results were disappointing.
However, this client is on Office 365, and 365 supports mail flow rules. It was very easy to configure a new rule to apply a disclaimer to all outbound messages (sent from this organisation) . Simply make the disclaimer text in html and paste it into the “specify disclaimer text” box – but watch out for outlook stripping margins on p tags  !
In order to further customise your new “signature” you can include a variety of variables pulled from the users 365 profile .
But wait …. iPhones were now sending the signature as plain text, replacing images with their alt tags. It seems this is deliberate behaviour on iOS, unless a message has a reason for sending html then it’ll send plain text. The solution was to give the iOS devices a signature of a single bolded space, deliberately pushing the message into html format . Then when 365 applies the disclaimer, it applies the html version.
It’s never as easy as you first think …
-  http://www.mail-signatures.com/articles/configuring-organization-wide-email-signatures-in-office-365/
-  http://apple.stackexchange.com/questions/53537/forcing-rich-text-by-default-for-ipad-iphone