Seeking a Mac HUD app with a CLI

I doubt this exists, but: I’m looking for a simple app that I can send commands to via a CLI that will show/hide overlay(s) above all other windows. The use case is that I have a few different keyboard modes that I toggle on/off via Karabiner and BetterTouchTool. But I have no visual indication that I’m currently in one of those special modes. It would be nice if when Karabiner/BTT triggers those special modes I’d also get a translucent banner along the bottom of the screen so I’d know that my keyboard was in one of those weird modes.