https://en.wikipedia.org/wiki/International_maritime_signal_flags#Letter_flags_(with_ICS_meaning)
https://en.wikipedia.org/wiki/Pratique
Pratique is the license given to a ship to enter port on assurance from the captain to convince the authorities that she is free from contagious disease. The clearance granted is commonly referred to as free pratique. A ship can signal a request for pratique by flying a solid yellow square-shaped flag. This yellow flag is the Q flag in the set of International maritime signal flags.[1]
Since flying the Q flag involves a request for boarding by Port State Control,[2] it has also become an invitation to Customs to inspect a vessel for dutiable goods or contraband, as in the "Rich Harvest" case, where a yacht carrying a large quantity of alcohol flew the Q flag in order to seek exemption from having to pay duty during a temporary visit to port.[3] The same vessel was also flying the Q flag when she was boarded in Cape Verde and found to be carrying more than one ton of cocaine. However, although the captain had thereby invited the authorities to make an inspection (being, according to his claim, ignorant of the fact that the boat was carrying contraband), he and the crew were nevertheless arrested for trafficking.[4]
Q Flag
VP Tie is Charlie Affirmative