Does indicator has corner mark?

[sonichy]

Something like:
this._indicator.set_corner_mark('1');

Extension (ESModule) | GNOME JavaScript

Dash To Panel Taskbar has corner mark:

[Sid]

I guess it’s a normal 'St.Label' with 'notification-badge' style class as shown in the following code.

• https://github.com/micheleg/dash-to-dock/appIconIndicators.js#L869-L905