When setting up your campaign email templates, you may notice that there is no signature at the bottom. That's because the signature is controlled and added by Google to the bottom of all your emails automatically. You probably already spent a lot of time getting that set up and looking just like you want it, so instead of making you do that work again, we just use what you've already set up!
Where to create or change your signature in Gmail or G Suite
If you'd like to create or change your signature, you can do that in the desktop version of your Gmail or G Suite Inbox under Settings > General, near the bottom. Here's a quick video to show you:
Did you know?
You can set up multiple signatures in your account - one for each "Send-As" address you've set up! If you have more than one address set up, just choose the address for which you want to create or edit a signature from the drop-down list above the signature edit window. Here's a tutorial to Google's help doc for how to set up "Send-As" email addresses in your Gmail inbox.