What does this traffic sign indicate?

You are correct. This traffic sign indicates a "Park + Ride" facility. In Germany, this means a carpark where you can leave your car and switch to public transport for the rest of your trip. Such parks are often located near train stations or public transport hubs to encourage people to use buses or trains instead of driving into the city. This helps reduce traffic congestion and environmental impact. The sign does not refer to a filling station or a car hire centre.