First, login to webmail with your email address and password @ http://webmail.brownrice.com
Click the "Settings" Tab
Click the "Identities" tab, then click your email address on the left
Finally, fill in the "Signature" box and click the "Save" button when you are done.
Note: You might want to fill in the "Display Name" field with your real name while you are at it. It'll make your outgoing emails look a bit more professional.