The signature in Gmail for iPhone/iPad doesn't have to be set specifically, the same design as for desktop will be used. If the signature doesn’t appear to the recipient, make sure you don’t have active a specific mobile signature that rewrites your default signature. To do that:
- Open Gmail app on your iPad/iPhone
- Go to Menu
- Tap Settings
- Switch Mobile Signature “OFF”
- Save your changes
Please have in mind that signatures in the iOS Gmail app are never visible while writing an e-mail but added to the message after sending. The signature might take up to an hour after the above described procedure to appear by the e-mails sent from the app. If you hurry, re-installing the app will make the signature appear instantly.
The Android Gmail app currently doesn’t support any signatures in HTML. However, if you open the Gmail site in your browser, the current signature will be assigned to your emails.