Measure it's diameter, if it's 1 and 1/8", I'd say it's a LC. You could always try tossing it in a tumbler with some other pennies to try to clean it a bit and see if you can get any detail off it.
You know, I thought that coin looked familiar after seeing the impact mark...
why oh why does everyone assume small round unidentifiable objects are electrical box knockouts?
do you see any rust?
does it look even remotely like steel?