How can I tell if a Gallery is missing a thumbnail?

Nimai

My current technique is to open up a folder in an incognito window, then I can see galleries without thumbnails as this:

But if I'm logged in, I see a thumbnail. This is for password protected galleries. Any ideas how I could more easily notice that I forgot to go back to Settings and set a thumbnail?

denisegoldberg

If you look at gallery settings the Feature image setting on the Basics tab won't be set.