International boat flags are also known as courtesy flags, The courtesy flag of the visited country replaces the yellow quarantine flag once cleared into port. International boat flags can also be used to display the heritage or nationality of the boat owner. Some international courtesy flags are the civil ensign of the nation, i.e., without the national coat of arms or emblem. Countries that specify the use of a civil ensign for marine use include Andorra, Argentina, Bolivia, Costa Rica, Dominican Republic, Ecuador, El Salvador, Guatemala, Haiti, Nicaragua, Peru, San Marino, Serbia, Spain and Venezuela. Use of the national flag that includes the emblem or coat of arms can be viewed as either improper protocol, or in some cases, illegal.

Display of Courtesy Flags & Foreign Guest Flags (ref; United States Power Squadron) If your vessel is without a mast, it should display the courtesy flag at the bow, in lieu of a squadron or club burgee, or on a starboard antenna strong enough to support it. If your vessel has one or more masts, display it single-hoisted at the outboard signal halyard of the main starboard spreader. Move any flag normally flown there to the inboard starboard halyard or, if your boat has only one halyard per side, to the port spreader halyard.

The customs observed in various foreign waters differ from one another. It is best to learn the correct procedure for the country you are entering. In some countries it is customary to fly the courtesy flag only after the quarantine flag (the yellow 'Q' flag) and the vessel has been granted pratique by the appropriate authorities.

Commercial Signal Code Sets contain 40 pieces including 26 alphabet code flags, 11 numeral and answering pennants and 3 substitute pennants. Signal code flags are available in three mounting styles: ash toggle with distance lines, brass grommets, or brass snaps & rings. All sets include a nylon storage carrying bag.

Signal Code Sizes
Size 0 = Flags, 1' x 1-1/4', Pennants, 2/3' x 2', Substitutes, 2/3' x 1-1/3'
Size 2 = Flags, 1-1/2' x 2', Pennants, 1-1/3' x 3', Substitutes, 1' x 2'
Size 3 = Flags, 2' x 2', Pennants, 1-1/3' x 3', Substitutes, 1-1/3' x 2-2/3'
Size 7 = Flags, 3' x 3', Pennants, 2' x 4-1/2', Substitutes, 2' x 4'
Size 10 = Flags, 4' x 4', Pennants, 2-2/3' x 6', Substitutes, 2-2/3' x 4'
Size 14 = Flags, 4' x 6', Pennants, 2-2/3' x 9', Substitutes, 2-2/3' x 5-1/4. (Snap and ring only).

Mil-Spec Signal Code Sets contain 65 pieces, acrylic coated nylon flags and pennants with distance lines, brass snap and ring.

Size 3 = Flags 5'9" x 5'9", Pennants 4'7" x 9'4". Size 4 = Flags 4'4"x 4'4", Pennants 3'5" x 6'11", Size 6 = Flags 2'11" x 2'11", Pennants 2'0" x 4'3", Size 8 = Flags 1'9" x 1'9", Pennants 1'2" x 2'5"

Signal code meanings and descriptions

International signal letter "Q" flag. On arrival at a foreign port, the owner or captain of a yacht (any size) should report to the authorities. The "Q" flag (plain yellow) should be flown where it can be easily seen: starboard spreader, radio antenna, fishing outrigger, etc.- to indicate that the vessel desires to be boarded by customs and other governmental authorities. When reporting, the crew and guests should remain aboard until permission (pratique) has been granted to land. Once pratique has been granted, the "Q" flag may be lowered, and the courtesy flag of that nation may be hoisted. Quarantine flags are not used for trips between the United States and Canada on the Great Lakes.