The letters found on stories are 'Content IQ' badges giving an indication of the relative usefulness of published content, where an A is higher than an E.
Hub keeps track of various types of user activity and also looks at how content is being used. This information is then used to give scores to both Users and to Content - the Social IQ and Content IQ scores respectively. Scores within a range are then converted into an associated badge, which can be displayed.
The setting can be found under tenant configuration > gamification >content IQ as per the screenshot below. Help guide section: http://help.bigtincan.com/help/configuring-the-content-iq-settings
The setting can be found under tenant configuration > gamification >Social IQ as per the screenshot below. Help guide section: https://help.bigtincan.com/help/configuring-the-social-iq-settings
If you wish to turn this off go to https://app.bigtincan.com.au/admin/configuration-bundles
Edit a bundle > UI section - uncheck show story/user badges
