In this article you can read more about Signatures and how to modify them:
Adding signature custom field
To create a perfect footer, you need to go to Settings → Integrations, choose your email account and click on Actions → Edit settings. There you can fill out your signature - if you use Gmail, you can even import your signature from there! Moreover, on the left hand side you can fill out all your sender custom fields as well.
Note: If you're using a Gmail email account, you can import the signature straight from your inbox using the blue "Import from Gmail" button.
Once that's done, you can add your signature (and other sender custom fields) in your message templates.
Adding logo to your signature
You can also add your logo to the signature - simply upload a picture to a hosting site such as Postimages.org, and in the signature creator click the image button, where you can paste the link to the image and define its size. Here you can read more about uploading pictures.
Voila! Your signature is ready to be sent!
After long tests we've come up with a couple of recommendations regarding the signature:
It's best to use only plain text - avoid using images, links and excessive formatting.
We highly recommend putting a phone number and the company's physical address in the signature as well, as it makes your messages look more credible.
If you want to link your website in the signature - it's best if the website is under the same domain as the domain in your email address. If it's not, we recommend setting up domain forwarding.
Under this link, you'll find our signature template: click!
Please note that those recommendations can improve your results and your deliverability, but if you're happy with your own signature, go ahead and test it to see if it performs well.