With the "Signature" block you can select any user and have their signature display in the email body. You can also edit the signature directly through the email builder and it will update in all the emails currently using the signature.
Click "Blocks" from the left navigation
Drag the "Signature" block and drop where you want it displayed.
By default it will be set to "The Contact's Owner"
Select which User signature you want to use from the drop down.
Add your information:
Upload an image, which should be at least 300px x 300px
Phone 1 Type (i.e. Office, Cell, personal)
Phone 2 Type (i.e. Office, Cell, personal)
Once you click "Save", your signature will be updated anywhere the Signature block is used, as well as update "Your Profile"