If you want to know how to add your email signature to Gmail app on your iPhone, follow the instructions below:
First, you will need to set up your email signature in your web-based version of Gmail. Once it has been set up in your web-based version, your iPhone will also automatically use the email signature. Follow our article on how to add a signature to your Gmail account here.
Wait a few minutes for the web-based Gmail server to sync with your mobile device's Gmail App. Your email signature will automatically be added to your email messages sent from your iPhone if you use the Gmail App on iOS.
Note: After installing your signature in the Gmail Desktop app, the Gmail server takes a few minutes to sync and update the signature across to the Gmail App on your mobile device.
Open the Gmail app by typing its icon on the iPhone.
Then go to the Main Menu.
Tap on your mail account to which you want to add the signature.
Then open Signature Settings.
Disable a default mobile signature. And that's it!
Note: There is no need to insert the signature here, as you already installed it on the desktop. It is going to be added automatically when you start sending the emails. This is normal if your email signature is not showing when you compose an email. You will not see your email signature in the Gmail App's email preview when creating your email message.
Please send yourself a test email or check the Sent items to double-check if it has been included.