Anyone have any idea what this little pin might be?

[e39_touring]

I found this sitting in the webbing of the block just rearward of the oil filter housing. It's a little less than 1/2" long (12mm?) and about 5/32" thick (4mm?). I had done the OFHG prior and cleaned this area out at the time, so it definitely happened on my watch. For the life of me, I can't figure out where this could have come from, but it bugs me!