German comedian Martin Sonneborn is well-known for jokes bordering on the tasteless. But a satirical political billboard of him posing in blackface makeup as US President Barack Obama is sparking outrage. “Ick bin ein Obama (I am an Obama),” reads the poster at Berlin’s central Ernst Reuter Platz square, in an apparent play on John F. Kennedy’s famous “Ich bin ein Berliner” speech. On the poster, a “black” Sonneborn smiles as he raises his arm in the air. The billboard is the latest in Sonneborn’s campaign for his satirical political party Die Partei ahead of state elections in Berlin this...