I checked all group permissions, including administrator, and all of them have "can mark items" and "can unmark items" unchecked. It seems to hide these options from showing next to the "Manage" and "Report" buttons on the item pages, but we still see "Mark Item" on the top right above the item pages under the "Unread Content" and "Mark site read" links. I tested it on the default theme and I'm using 4.4.2.