Gmail's Web interface allows you to add a signature that appends to your messages. Fortunately, the mobile application also supports this. What's the importance of adding a signature? For starters you can make those you e-mail a bit more forgiving to your typos, or perils experienced with autocorrect, if you simply add "Sent from my phone" to each message. Alternatively, you can add the same signature that your e-mails sent from the Web interface contain, so those you e-mail will not know where it was sent from.
1. Open the Gmail app on your phone.
2. Press the Menu button and choose More.
3. In the new menu, select Settings.
4. This is the main settings area of Gmail. Take the first choice in the list, Signature.
5. Enter your custom signature and press OK. Your signature will be saved and appear at the end of your future Gmail messages.
One note: a savvy Web user can still figure out whether you were really at your desk, so don't try to trick your boss without being aware of the consequences!