quarantine flag

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quarantine flag

(Nautical Terms) nautical the yellow signal flag for the letter Q, flown alone from a vessel to indicate that there is no disease aboard and to request pratique or, with a second signal flag, to indicate that there is disease aboard. Also called: yellow flag or yellow jack

Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014

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As you enter each port, fly the yellow quarantine flag and notify Customs of your arrival.

Bottoms Up

I have never seen the yellow quarantine flag of the U.S.

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At the port, you are instructed to fly the yellow quarantine flag and notify Customs of your arrival.