In order to save pinned items in "My Favorites", you first need to sign in to BU Libraries Search.
After you type in your first search and are looking at the results, sign in by clicking the "Sign In" button in the upper right of the page. You will then be asked for your BU user name and password. If you have already signed into BU during your current browser session you will not be asked for your credentials again, but it is still necessary to click the "Sign In" button to sign into BU Libraries Search.
You will also see a sign in reminder in a yellow bar above your search results.