It was one of the gold addons, but reddit is using the gold subscriptions as sort of like buying early access to beta features, rather than as a set of purchased features. When new features are built, gold members get first access to them, then when they're solid / when a new batch of new features comes in, the old gold stuff goes public and gold members get access to the latest features first, ad infinitum.

The logo title text was rolled out to public users last week, when reddit introduced a feature to gold members allowing them to have new comments added since their last visit to the page flagged as such.