What does this traffic sign indicate?

Your answer is correct. This sign indicates a natural gas fuel station, specifically for CNG (Compressed Natural Gas). In Germany, this blue sign with "CNG" informs drivers that they can refuel vehicles powered by natural gas at this location. It does not refer to a hydrogen or auto gas (LPG) filling station. Recognizing the difference is important, as each type of alternative fuel has its own designated sign and abbreviation. Look for the specific marking "CNG" to identify a compressed natural gas refueling point.