In order to add a link to your Storefront to all your new auctions, please click on the My Account tab, then Storefronts, and then select the following option:
"Promote and Increase traffic to my Storefront. Include a Storefront
banner in all of my auctions."
Click "Save Preferences", and any future auction that you create through Auction Manager will contain your Storefront link. (Please note that the link will not appear in any existing active or pending auctions, or auctions that are relisted that did not initially contain the link.)