When a block is broken in a layout, we show a red message as the block description:


...but there is no hint whatsoever elsewhere. I would expect that red color to "propagate" back all the way forming some sort of trail that the site admin could follow. So there should be a site status error too that triggers the admin bar red badge to show:


...and then on the manage layouts page, the layout name (and perhaps the template icon too) should also be red:


GitHub Issue #: