In the olden days the yellow quarantine flag, or the Q flag, had to be flown by all vessels with an infectuous disease aboard. Today, it’s the other way around. A vessel entering the territorial waters of a country must fly the yellow flag on the starboard side of the mast to signal to the port authorities that there is no disease aboard and that the vessel and its crew are ready to clear in, i.e. to undergo the customs, immigration, sanitation, decontamination, taxation and any other bureaucratic formalities to obtain a document called Pratique. Clutching the Pratique firmly in his hand, the captain and its crew can now roam freely the territory and the territorial waters of that country.