Installed PWAs can set little badges on their app icons.
WebKit recently posted an awesome article about doing it on iOS: https://webkit.org/blog/14112/badging-for-home-screen-web-apps/
And I recently wrote some docs about it on MDN: https://developer.mozilla.org/en-US/docs/Web/Progressive_web_apps/How_to/Display_badge_on_app_icon
By the way, there's more work to do on this MDN page if you're interested, here's an issue: https://github.com/mdn/content/issues/26430
@patrickbrosset An a new developer in training and blogger of 15 years, I would love to take this update! Looks like a “good first issue” to me.
Can’t say I’m confident about the process and expectations, but willing to give it a go today. 
@kevinctofel great! Feel free to show your interest on the github issue and people should start showing up to help you along!
You can also take a look at the contribution guidelines https://github.com/mdn/content/blob/main/CONTRIBUTING.md
@patrickbrosset Thanks! Left a comment there indicating I’d like to work on the issue. I’ll fork later today and get cracking unless I hear otherwise. Appreciate the guidelines too. I knew about them but you reminded me to review them before I do anything else. Cheers!