How can I add an automated signature to my emails from my Droid?
For Gmail: open the Gmail app, hit the menu button, go to Settings, then Signature. You can use multiple lines for your signature.
By default, the app doesn't add the standard "--" for message separation like Gmail normally does. But you can add it yourself and it will appear the same way to other Gmail users.
In the standard email app, it cannot be done. As a work around, I edited the "Your Name" field (Email App > Choose Account > Menu > Account Settings) to read "Josh - Droid" instead of just "Josh."
You could edit it to say "Josh - Sent From Droid," obviously substituting your name in there. Its not glamorous, but gets the job done.