Gmail app on iPhone allows users to use the signature set on the mobile device instead of desktop. You can use this feature to let know recipients that you are mailing from mobile device instead of desktop.
Step 1: Launch Gmail app on iPhone and tap the details icon.
Step 2: In the details screen, tap the Setting icon available after your email address.
Step 3: In the Setting screen, mark the checkbox with label as Use mobile instead of desktop signature. Then enter the signature text by replacing the “Sent from Gmail Mobile”.
Now when ever you send an email from the Gmail app, the mobile signature will be part of the email instead of desktop signature.