Unidentified Token / Coin Planchet

@fir, my first thought is that someone countermarked an arcade token blank.

The stamping of the "D" on both sides implies this is deliberate and intentional, rather than some random dude with a metal punch kit. The "D" meant something significant enough to whoever put it there. Unfortunately, removed from its context, that story is most likely impossible to recreate.

I would concur that the rim looks more like a completed coin than a coin blank; that would make the original un-D-punched object a blank generic token. Many token-makers sell such blanks.