In maritime history, one of the most enduring images is the pirate flag known as the jolly roger, featuring a skull and crossbones. This custom boat flag was utilized by pirates to declare that the ship was being crewed by brigands and would give no quarter when engaged in battle, and most often was flown to scare other ships.

Maritime or boat flags are a language all by itself. As flags are enduring symbols, and the maritime world has etiquette for its flags.   Ensigns are often called to be hoisted upon entry and departure from harbour, when travelling through international waters, and when the vessel is called to do so by a warship. Jacks are other national flags which are being hoisted by warships at the front of the vessel.

They often fly these flags while the vessel is not travelling and when it is decorated during special celebrations. The rank flag, also called the distinguishing flag is the one hoisted by an officer of higher rank on his flagship or territory, thus called a flagship. The pennant, or called a pennon in the olden days, is a long narrow flag which signifies various interpretation bases on its design and usage. Merchant ships usually hoist a flag showing which company holds ownership of the vessel.

Members who have membership to a yacht club or sailing group can fly their club's distinct burgee, a custom boat flag,  both while underway and at anchor (however, not while racing). Historically, when a member of one club goes to another club for the first time, they usually exchange one another’s burgees. The burgees are subsequently shown on the grounds of each club, which can be club office or bar.

Today, boating enthusiasts have created their own custom boat flags, and fly them from their power boats or yachts. As sailing organizations become more popular, the demand for custom boat flags has led custom flag makers to include them in their product lines.