Warning when image isn't full screen

When editing with photos and videos often we’ll shrink an image on a top layer incorrectly (v1 for instance).  [Think 4K video on 1080P timeline 48% scale - the image on top does not fill the screen completely].  But because V1 image might be dark and it’s over “system black” (default layer) it’s tough to see.  

We then export the video and only notice that V2 isn’t sized large enough when watching playback.  So we need to go back into Premiere and fix. 

When working with a lot of image resizes I often make an orange colored background and put it on v1, then do the rest of the editing on the layers on top (V2+).  If any are not sized correctly I’ll see the orange and know to fix.

Perhaps something like SAFE MARGINS that you can click on and off, yet doesn’t show up in the actual output.