Not exactly true either. The panner options depend on if the group is routed to a mono or stereo bus. So a stereo group routed to a mono bus will not show panner options despite the group itself being stereo.
The puzzle is still not solved then…you guys do know your Cubase inside out!
You’re right. Then the solution to problem would be Edit channel, Show output chain. Don’t have to righ-click the panners, just hover mouse over them, there’s an arrow on the right side of the panner if it’s a stereo.
How about that mono/stereoswhitch? 
Edit: Or go to VST Connections Group/FX where you can see them all directly!!!
+1
yeah … Maybe labels will come back into fashion one day.
It’s not ideal but start track name with So or M. As I say, not ideal but it works.
When in question the Stereo Balance/Combined Panner is how I do it, usually all my mono channels are set up the same always for certain instruments (Bass, Gtr, kck, snr etc) and I never think about it. Now that you mention it would be great to have mono - stereo switching available, the indicator in mixer would be nice too
Have also been looking into this…
To make REALLY sure if a group is mono or stereo, I open the channel edit window and switch “Inserts” from “Plugins” to “Routing”. There will either be one or two streams displayed. 
I see this as a workaround though, a little circle or doublecircle symbol on the channel shouldn’t be too much to ask for!