Can I put a Mailing List button in my footer?

Yes. In the website editor, open Footer and choose Links. Under Buttons, click + Add button, type Mailing List as the Display Label, and set Type to Member Popup. The button then opens your signup pop-up, where visitors join your list. The pop-up's heading, message and which list people join are in Site Settings, Email Popup.

A footer button can also go to a page, another website, or a file. These buttons show only in the footer. To show your header buttons in the footer as well, set Repeat the header buttons in the footer to Yes on the footer's Settings tab.