Admiral Nelson is famous for putting his telescope to his blind eye so he could claim not to have seen an order, relayed by flags, from his commanding officer.
Fortunately for him, that adventure turned out rather well.
You'd think that in this age of advanced telecommunications signal flags would have gone out of use, but they're still widespread, important, and even in some cases obligatory. This one, for instance:
means I require assistance.
means I have a diver down; keep well clear at slow speed.
means I am disabled; communicate with me.
These flags are also the V, A and F flags, respectively, and they can also either be used to spell out messages, or they can be used in combination as a code message.
There have been, and are, several languages of ship flags. There are special codes for NATO warships, and others for racing yachts and fishing vessels.
is one which Nelson himself sent before the battle of Trafalgar: England expects that every man will do his duty. This message is in Sir Home Riggs Popham's Telegraphic Signals of Marine Vocabulary. As you can see, all the words are available in code except for DUTY, which has to be spelled out one letter at a time.
Finally, here's an example of a message consisting of the three alphabet flags we started with. Here it's been made to be worn as a brooch.
The letters, as we saw above, are AVF, but the signal when combined?
Permission to lay alongside.
Thing To Consider Today: what message your own badge might say. The word signal comes from the French seignal, and before that from the French signum, sign.