Daniel,
I don't know too much about the holster but the back is marked "Audley" with two patent dates of March 1908 and July 1925.
It can be used as a back pocket holster and secured using the button tab. Some of the old baggy men's pants had a button on the back pocket and were deep enough to accomodate the holster.
I just noticed in looking at the holster that it also has a loop in the top for a thin 1" belt.
One of the other forum members, Lefty, is very knowledgeable of these "old police style" holsters. Maybe he'll be able to add some more info.