Hoping somebody can help identify this part. It's a 1 x 2 brick, but has a square hole on one side. Many a part has got me stuck, but rebrickable has helped me many times. Can't seem to find this one.
Like @JohnnyB commented, this is the lower part of 76385 Hinge Brick 1 x 2 Locking with Single Finger On Top:
Well, between my comment and zovits "seconding" the idea, I think it's safe to assume we've established what this part "was". I did a lot of searching earlier online, looking through people's collections of non-production and prototype rare parts and couldn't find this "version" of the part. So, whatever the story of how it came to be, I would certainly consider this to be a rare keepsake. Here is a photo of the inside of these bricks with the square insert from the "finger" easily identifiable.
I couldn't bring myself to attempt a disassembly since I apparently don't have many of these and they aren't the more common color of Black and Dark Gray. Perhaps Rin Rio-Oki will happen upon this question and take the initiative of dissecting one? Fingers crossed ;)