I suspect it
was once an allen screw. Maybe a torx (I have lots of those in multiple sizes). I could fit one of my small allen keys in there but it wouldn't budge. Then it slipped in the head a wee bit - I think that glue is also on the threads of the screw. I don't have high hopes of getting that little goodie off.
I have actually been behind the fridge - thinking to tap into the purple 12V line (water pump, toilet, furnace - since the toilet is no longer there, and the furnace runs almost never and the pump intermittently - best line to use I thought) for my power to the cell booster (decided to mount the booster on that fridge wall and either run the power back from one of the reading lights on the front cabinet, or from behind the fridge - a different story
)
Was looking for where that hole next to this thing came out back there. Found the hole, but haven't explored farther into the space to check for the back of the screws. Going back today and I'll do a check. However I did find a cut-off toggle screw back there. I suspect there was some attempt at mounting that little hunk of hardware just using a screw through the wall and it pulled out. Hence that remnant hole. We know there isn't much "wall" there. I'll bet when I manage to get my hand far enough back, I won't find much. My guess is that they cut the screws off (also found some pieces of screw thread that had been cut off with a side-cutter). And therefore that little piece of "whatever" is glued on.
My plan for the booster amplifier is to use the velcro that is on the back of the snap on base, and pop it off the base when I'm traveling or not using it (which will be most of the time). Don't need to have it bouncing along while on the road and putting stress on the wall.