Learn here how to add or change an email signature that goes at the end of an outgoing email:
Go to Settings, then on the left, Mail, Contacts, Calendars.
Scroll down a little on the right hand panel, and select Signature.
You should be able to select an option “per account” meaning that it will use a distinct signature for each email account.
In the box below that, type in the text you'd like to have at the end of your email messages.