Adding your Gmail signature to an Email Campaign is as easy as checking a box. If you aren't familiar with the steps to create an Email Campaign, first review our guide, How do I create an Email Campaign?
Then, follow these steps:
1. After you decide on a template to use in your Campaign, select the Edit button for that template on the far right of the Templates screen.
2. From the Edit Template screen, check the Use Signature box. Then select the Save & Merge button.
After taking the above steps, your Gmail signature will be included for the current Email Campaign.