Add a signature and date line to node print template?
Add a code field to Display Suite that is visible on nodes, and add your HTML to the code field.

Place the field last for the specific view mode, and make sure to assign a class (or assign the class directly in the html of the code field) on outer html element.

Test that the html is displayed on node view (normal page view).

In you theme's style css (css that targets web page view) set the display of this class to none. Now it should only show for print. If it does not go into your theme's print.css file and set the display to block or whatever you prefer. If there is no print.css (highly unlikely) then just add a @media print rule to your css.