I'm posting this on behalf of an internet acquaintance from Canadian gun forum. It was his grandfather's gun but beyond that the history is unknown. This front sight is smooth on the opposite (left) side. The wooden device was formerly strapped to gun with leather however the strap now detached. Whether the owner competed in shooting sports is speculative but seems likely. Am wondering if anyone has seen something similar or can shed a light?
The gun itself is an EC Green with T. Conway of Manchester address on rib
The front sight is a "Gilbert's Two Eyed Sight" to prevent cross-firing
Greener's "The Gun and Its Development", 1888
https://books.google.com/books?id=LAsAAAAAQAAJ&pg=PA531&lpg 
Modern Meadow Industries Sight-Blinder Crossfire-Reducer
I think it is unlikely that the breech device was attached for wing or inanimate target shooting.
We might as well make this thread thematic
On a Parker try gun, and I suspect for the fitter; looking toward the shooter's eye from the muzzle end
Like Oliver's Sight-Aligner
On a Parker Live Bird gun and I have no clue as to the point, pun intended
or Chapek's Leader Gun Sight
https://books.google.com/books?id=Zd4DAAAAMBAJ&pg=PA44&lpg
Wilbur Gun Sight possibly similar to the original post
October 1919
Forest & Stream https://books.google.com/books?id=F99JAAAAYAAJ&pg=PA568 
The Nydar Shotgun Sight, Model 47 Receiver Mount was made by The Swain Nelson Co. of Glenview, Illinois. It was developed near the end of WWII, and marketed to sportsmen early 1946.
And this "bright" device for those who shoot with both eyes open
The Monopeian in Greener, "The Gun", 1907
https://books.google.com/books?id=3HMCAAAAYAAJ&pg=PA412 
Popular Mechanics April, 1951
https://books.google.com/books?id=AdkDAAAAMBAJ&pg=PA256&lpg 
Lots of variants since to enable shooting from the right shoulder but with the left eye.
Carey Sidesighter
First Parker I bought when I had more cash than knowledge. A VHE 12ga on a No.1 frame. I can only imagine it was set up for deer hunting with slugs...chokes cut out, recoil pad added, bulged barrel and rudimentary rear rifle sight.
Drew, thanks so much!
Happy New Year's to you, sir.
John
Some of those sights for mounting the gun on the right but shooting with the left eye (or vice versa) are very much like the system devised by Dave Fjelline after his eye accident a few years ago. Anyone who has seen him shoot since would certainly not believe he had a handicap...
I know a fellow who mounted a one inch diameter tube on the left side of his shotgun as his right eye went bad. He shoots sporting clays and does quite well. Do what works!
Happy New Year to all, even those who think I am a dumb Colonial!
The wood block looks like a trap shooting and or sighting device.
The eye would site through a different notch at each station.
CZ, think about a right handed shooter trying to line up with the right side notch in that block. It would not be easy.
I don't know what those notches are for, but my guess is that this is a prototype from a failed experiment.
What can I say?
When they teach trap shooting they divide the trap house into 5 sections.
You line your eye and barrel up over each spot.
5 slots on that bridge seems obvious to me.
That kind of had the look like trap shooting to me also. I think the wood block would have been asymetrical if it were for a one eyed, cross eyed shooting.
Maybe, if there's no finish color difference under the wood or rub marks where the leather would have cinched down, it might not have been on the gun much. Just on appearances, the outer notches don't look like the comb of a stock would be much use. But, maybe the thought was built in lead and high impact point for spot shooting if someone could get it all sorted out quick enough when the bird shows?
