Bill sent us this picture of his unusual coin. It is a pattern coin, struck as a trial piece before any were issued for circulation. No such 100 reichsmark coins were ultimately issued. Hitler's profile never appeared on a coin issued by the Third Reich, just as well. (Excuse my political commentary!)
That's the Brandenburg gate on the reverse side of the coin. Bill also supplied a catalog page (I am not sure which catalog) that shows the coin as Bruce number X94, with no KM number, mintage, or estimated value. It shows the coin as minted in 0.333 gold.
High quality pattern coins like Bill's are usually eagerly sought by collectors. This coin is probably no exception. For instance, you can see a nice set of patterns for sale at this link to the MA Shops and this link at VCoins.
To get an idea of value, CoinQuest wrote to several experts on German coins. Bowers and Merena galleries estimates a value around $1500 US dollars and ultimately backed up their estimate by offering Bill that much. As far as I know, Bill sold his coin to Bowers and they sold it at auction.
Another coin catalog notes that these were 'Possibly produced in Buenos Aires, Argentina in 1959 as souvenirs for German veterans.' This catalog lists the value at $3000 US dollars for coins in fully uncirculated condition.
DO NOT CLEAN YOUR COIN, BILL. CLEANING RUINS VALUE.
Try not to handle it and never put your fingers on the face of the coin. Handle it only by the edges.