This 12" x 18" Yellow Quarantine Flag is also known as a courtesy flag. Its use is for boaters to signal their entry status into foreign countries via sea. The flag signifies you have entered foreign waters but have not yet cleared customs in the country they are entering. Flag etiquette for small boats entering the Bahamas is as follows: If US registered, fly the US Ensign on your starboard outrigger or radio antenna. When within sight of land in the Bahamas, run up the yellow quarantine flag on the port outrigger, signifying know you are in Bahamian water and have not yet cleared. After clearing into the islands, replace the yellow flag with the Bahamian courtesy flag, which now signals your home country and that you've cleared into the current one. When returning to the US, temporarily replace the US flag with the yellow one, until you've cleared Customs there.