Hi Alan,
You sure seem to have an eclectic collection, with pretty intriguing examples!
Although I think this one also exceeds the ethnographic scope, I will note what I can and then think we should park it, OK?
I think you got it pretty close with the similarity to Civil War regulation military medical and payroll swords, as the crossguards are primarily the same but usually with corresponding lettering in the shield escutcheon. In the Mowbray reprint of the "Ames Sword Company Catalog" of c.1881-83, there are also 'rapiers' (in 'neoclassic' fashion) of this type that correspond more closely to the hilt on yours. While the crossguard, scrolled quillons and shield escutcheon are essentially the same, the fluted grip bolster and studded ring as seen on your example are more like numbers 622 and 623 in the book.
These are shown as intended for military associations, with one listed as for the New Haven Grays (the shields on these have those initials). Also the grips are wire wrapped black and the pommels are more ornate and military.
On the grip, which is of bone, I recall that many years ago I had a M1840 NCO sword stamped Collins & Co. which was extremely unusual in that it also had a bone grip much like yours. Also, the regulation pommel was gone and a much simpler cap had replaced it. It may be possible that an 'aftermarket' cottage industry of rehilting these with the attractive bone hilts might have existed around the end of the 19th c. Your example may be one of these association types produced c. 1880's and rehilted, much as the one I had, as regalia in either fraternity or association? I always thought the one I had was pretty neat, as I never saw another with the bone hilt.....now I have
!
Hope this helps Alan...keep the ethnographic stuff comin' OK !!!!
All the best,
Jim