The markers are in a new column to the right of the album title. They also appear in the bottom left corner when a Discover Weekly track is playing. We were only able to see the new icons on the desktop app, but we expect that the feature will also be implemented on mobile if Spotify moves forward with a full rollout.
Based on the early tests, it seems that using the buttons would add some more direct control over what will appear in the following week’s selections. This could be useful for people who want to curate their recommendations to avoid any guilty pleasure listening, or who might have somebody else using their library.