Has anyone ever seen this before?
That does not look like a fire lite cabinet based on the lower left corner. I would say it’s something someonme made.
Sweet custom work, looks UL listed (sarcasm) And the MS-4 board is pretty small if you dont need room for batteries.
Hopefully this isn’t protecting anyone or something important
Interesting small sized panel.
Oh, you know…just a building. Made entirely out of wood. 
Here’s a better shot…
IDK why I didn’t post this in the first place.
Battery cabinet could be located somewhere else 
What if they’re maybe using it as an annunciator? Maybe they rigged it to work like that…
That isn’t possible with an MS-4. They probably mounted the board into the cabinet of a previous panel to avoid disturbing the woodworking. It’s done a lot, but someone actually took the time to make it look nice in this instance.
Looks like that’s an FCI CLP-4 cabinet, indicating that the MS-4 is indeed most likely installed in the previous system’s enclosure.
I think you’re right! The system has FCI MS-2s everywhere, and upgraded to an MS-4 a few years ago.