The 20-mark gold coin, a safe bet
20-mark piece, Frederick I, German Emperor, 1888, German
European influx of fakes
German 20 mark coin (Gold mark), Currency Wiki
Germany, Prussia - 20 Mark 1906 A - Wilhelm II - gold - Catawiki
Xf 1906 A German 20 Mark Gold Coin Wilhelm Ii
20 mark 1906, German Empire - Coin value - uCoin.net
20 mark 1890-1913, German Empire - Coin value - uCoin.net
Here is a 1905-F 20 Mark gold coin from Germany/Wurttemberg. This coin features Wilhelm II and the mintmark F, denoting Wurttemberg, on the obverse.
1905-F Germany/Wurttemberg 20 Mark Gold Coin Wilhelm II NGC Uncirculated Details