It is currently not possible to target "all android devices", only for some.

Certain manufacturers (e.g. Samsung notably) have included this functionality into their customised Android launchers. Also some 3rd-party launchers (e.g. Nova Launcher) have included an API to accomplish this.

Stock Android does not offer this functionality at the moment on the standard launcher.

I have just seen that this is a duplicate of:

• Is there a way to add a badge to an application icon in Android?

There are many other related posts about this type of thing:

• How does Facebook add badge numbers on app icon in Android?
• https://***.com/questions/18205569/does-samsung-modifies-its-android-roms-to-have-badges-on-email-and-sms-icons?rq=1
• adding notification badge on app icon in android
• How to interface with the BadgeProvider on Samsung phones to add a count to the app icon?
• How to add a notification badge/count to application icon on Sony Xperia devices?
• How to make application badge on android?
• How to display count of notifications in app launcher icon

You can find more information there.