Original "Red Mottled Grips"
In my opinion the grips are original factory "Red Mottled Grips".
The appearance is exactly what I personally would expect to see with grips this old on a gun in this condition.
The wear pattern mentioned is also familiar to me personally. Family history of law enforcement dates back to the late 1800's.
My grandfather had a quick draw rig called a "Clamshell holster" that was actually made here in California. I kick myself often when I think about that rig because it was lost and even as a kid after Grandpa was long gone and playing with it with my older brother, I saw the historical value in keeping that rig.
Anyway, water under the bridge...... Common problem with that old rig was the spring would weaken after many years of field use, the internal lining would wear, and the gun would slip down lower than normal with the grips riding on this spring-loaded nub, resulting in a constant rubbing on the grips. That's exactly the marking that was on my grandfather's 38 revolver. Not quite the same location and his gun had wood stocks, but the same rubbing worn pattern as I remember.
This large frame DA dates to the 1880's. Lacking a logo on the frame. This gun has been there and done that. I like it a lot. I hope the OP gets it so we can see more photos.
Murph