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Your extractor-grade boxlock (as opposed to being a sidelock) 20ga SxS with the straight (English) grip appears to be a European-made field grade gun - as indicated by the underbarrel sling swivel eyelet.
The important identifying marks on these are usually hidden, stamped into the bottoms of the barrel(s) & barrel flat(s), and on the action watertable flats.
Those areas are only visible by removing the barrels via pushing the button on the front of the forend, removing the forend by pivoting it down/off, and then unhinging the barrels after holding the opening lever to the right.
Closeup pics of the marks/stamping found on those areas might tell when & where it was made, and might also contain a maker's mark - besides the serial number.
A European-made gun will have those marks (proofmarks) by law; American-made guns usually won't.
The "S" on the top tang, between the opening lever & the safety button indicates "safe" : If the "S" can be seen, the gun should be "on safe" (if the safety's working properly), with the gun/triggers blocked & unable to fire.
When the safety button/slide is moved forward, "off safe", the "S" will be covered from view, indicating the gun is ready to fire (not safe).
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