A black circle centered on a yellow background, India stands for "I" in the signal flag alphabet. Ironically it looks more like a bizzaro Japanese flag than an Indian flag, but I think that'll be enough to help you remember.
India means the vessel flying it is altering its course to port (Echo's counterpart). Again, pretty useful for knowing which way the ship coming directly at you is turning. Helpful tip - if you see this flag, you should turn to port too, not starboard. Otherwise you'll run into each other!
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