HooYah Deep Sea
If I may, for CapnMac,
You may indeed. Especially as I managed to invert Hoist and fly in the above. Sigh.
That image exactly renders a swallow-tailed signal flag.
In the days of sail, the flags and their pennants used a wooden toggle at the top and an eye at the bottom. These were replaced with rings and snap hooks.
Been gabbing with the old bubleheads I know. And, even being as ancient as I, none are old enough for "pig boat" service. But several were noting that the diesel boats were sent out with "PT Boat" flags sets (e.g. #7 or #8), rather than Destroyer/Escort sizes (e.g. % & 6).
Several have noted that it was going to be rare to have a Diesel boat on a Buoy or in and anchorage to where they'd need to fly their Radio Call Sign. Rafted up to a pier or Tender, you can send messages by Runer, rather than radio.
It's become rather an interesting scavenger hunt into history. (Isn't that why "we" do this--just an excuse to buy more books, as Bill signs it?)