You decide. If you opt for the terse and more immediate mobile tapping, you don't have to compose wordy excuses (for concision and overlooking inspiring auto-corrections) every time; you can set up a special signature (in addition to your normal Gmail signature) for Gmail's mobile web app instead.
Set Up a Signature for Mobile Use in Gmail
To add a special signature for the Gmail mobile web app:
- Go to the label list in Gmail mobile.
- If you are viewing a label — your inbox, for instance —, tap the list icon or Menu.
- Select the gear button at the top right.
- Make sure Use mobile instead of desktop signature is checked.
- Enter your mobile signature in the text field.
- Tap Apply.
(Updated April 2012)