Boat flags or signal flags have been used since Roman times. Originally they were used to send messages to both ships or to people on land concerning the vessel at sea. This is called Flag semaphore, which is a system of flags, circular paddles or even hand signals. The semaphore system differs from the international code system. The Semaphore system uses 2 square flags that look identical, one held in the right hand and one in the left. The square flags which are red and yellow are divided on a diagonal. The hoist edge is red and the fly end is yellow. This system uses two flags held in various positions resembling the face of a clock. For example, if you wanted to signal the letter “R” you would be holding the flag in your right hand at a 9 o’clock position and the one in left hand at the 3 o’clock position. Each letter of the alphabet and has different “clock” positions. There are numbers 1-9.
This is what the Semaphore Alphabet looks like: