To configure your signature:
1. Access your account settings
2. In the Usertab, go to the Signature section.
3. Click on Edit at the bottom right of the signature.
Signature templates
Select one of the signature templates available and save

Personalization of the signature
In the window dedicated to customization, you can :
customize the text
integrate links
integrate images
edit / change HTML

We advise you to use a signature without images for your sequences in order to increase email deliverability.
Too many clickable links may disperse your prospects when reading your emails. Unless the link that is in your signature redirects to a landing page with a form, and that would be your call-to-action :)