keyhole escutcheon, awesome design. I wasn't able to find that specific plate on any of the reclaim sites I frequent.. are there any markings on the back? Could possibly date from 1880s-1910? I have backplates for my interior doors that are dated 1889 with countersunk screws.
(Just a note, even very simple escutcheons from that time period retail for $15-25.. the ornate and rare I've seen upwards of $75)