macOS High Sierra
Add Messages to the menu bar
You can add a Messages menu to the menu bar so that you can manage your online status and see which buddies are available for messaging, even when Messages is closed.
Choose Messages > Preferences, then click General.
Select “Show status in menu bar.”
If you don’t see this option, you haven’t set up a Jabber account.
Click the Messages icon in the menu bar, then do any of the following:
Set the status of all your active accounts: Choose a status from the menu.
Send a message to an available buddy using an active account: Choose a buddy from the menu.