Just yesterday, YouTube announced via their Team YouTube channel and Twitter account that they are rolling out a new analytic card in their YT Studio for the creator’s subscriber bell notifications.

The new card can be found in a channels’ Analytic menu under the Build an Audience tab.

The card shows two data points regarding the Subscriber Bell and related notifications. Firstly, it shows the percentage and number of subscribers who have “rung the bell” – turned on “All notifications” for the creator’s channel. Secondly, it shows a sub-set of that number who actually have notifications turned on on their YouTube app or desktop notifications.
YouTube also provide “typical” percentage for both so you can get a feel for how well you’ve communicated the importance of “ringing the bell” and turning on notifications in their app/device.