What does this traffic sign indicate?

Your answer is correct. This traffic sign indicates a customs point ("Zoll" in German, "Douane" in French). It means that vehicles must stop for customs control at the border. It does not mean a toll road or a prohibition on through-traffic. You will see this sign when entering or exiting the country where customs checks are required. If you encounter this sign, make sure to stop and follow any instructions given by customs officers.