That flag looks like a number 7 Naval Ensign made for or at the New York Navy Yard. Brass grommets and reenforcement in the upper & lower hoist follow the Navy rules for an ensign. The size also matches the Navy Yards number 7 U. S. Flag. This flag was more then likely custom made by Annin & Co. and used as a reunion flag for the 7th Regiment, late 1800 or early 1900.

Happy Trails!
Tom Martin