What does this traffic sign indicate?

Your answer is correct. This traffic sign indicates a natural gas (CNG) fuel station. CNG stands for Compressed Natural Gas, which is used as an alternative fuel for vehicles. In German traffic rules, this sign helps drivers identify stations where they can refuel their vehicles with natural gas. It is important to recognize this because not all fuel stations provide CNG, so this sign guides drivers of CNG vehicles to the appropriate refueling points.