Many Automation Rules are triggered by user operations through the Browser, and it'd be interesting to be able to notify such users on the result of the automations they just triggered.

The AJS Flag mechanism could be used:
https://aui.atlassian.com/aui/latest/docs/flag.html
AJS.flag currently allows Info, Success, Warning and Error messages.

As a workaround, Automation Rules can send an e-mail or add a comment to the Issue (even mentioning the user), but the quick notification popping up right on the visible screen is harder to miss.