Thank you for this info! So are there combinations of these flags?, and I'm naively spit balling,, the flag shown in my op could be 1st division red disc on an artillery brigade red flag, with headquarters swallowtail?
Or was that not even a thing lol
The commander's marker flags had a very important tactical purpose. At a glance, the position & unit designation of commanders could be ascertained.
For example, the white flag with a red disc belonged to the commander 1st Division, 1st Army Corps. Even at considerable distance that message came through.
The point being that the success of the Butterfield system was a function of its elegant simplicity. Modifying a marker flag, as you suggest, would only sow confusion.
Your example is not an international maritime signal flag. Nor is it a yacht club flag.
American Yacht Club flags from Lloyd's Register
It is not the house flag / funnel marker of a shipping company.
We know what it is not; what is it? There is one highly speculative possibility.
I have no reason to believe that you have a Civil War era flag. That being said, artillery batteries carried flank marker flags. Like the example below, they were (+/-) 24" on the fly. (Length)
Link:
These purple, silk swallowtail flank markers include a painted regimental identification. To create the swallowtail, a horizontal cut was made from the fly edge and each end was then folded and stitched along the vertical, turning under the raw edge. The top and bottom edges were then turned up...
museum.dmna.ny.gov
In the Army of the Cumberland, the only army I am familiar with, artillery flank marker flags were handmade, not from a depot. As a result they were not necessarily of a regular pattern.
The only one that exists today is from the Chicago Board of Trade Independent Battery of Light Artillery. It is a rectangular red flag with CBT in yellow paint on it.
I suppose your flag could be an informal flank marker. If so, it would be very rare.
Odds are it is a modern pennant for a ball team or such like.