The largest German cities generally only have one letter codes ( B = Berlin , M = Munich , K = Cologne ( Köln ) , F = Frankfurt , L = Leipzig , S = Stuttgart ) , most other districts in Germany have two or three letter codes .
For example , the urban district Regensburg has more citizens than the rural district Regensburg , so the city has two letters after the code R . The number of letters in the city\/region code usually shows the size and location of the district : the largest German cities generally only have one letter codes ( B = Berlin , M = München ( Munich ) , K = Köln ( Cologne ) , F = Frankfurt am Main ) , most other districts in Germany have two or three letter codes .