Forum sends you emails. Your system already shows when you have emails. Problem solved.
An alternative could be to define that topics I post in would be set to "Receive E-Mails" instead of "Receive Alerts".
The difference is that I know that I only receive alerts in the Arduino forum. An e-mail can be from anywhere/anyone.
Yes, you can do this via Profile > Forum Settings > Settings > Notifications > Notification Preferences.