Without part numbers or markings, it would be hard to tell if it came from a specific aircraft. I many cases, parts like that could be used in multiple types as well.
On warbirds today, sometimes the plexiglass piece is there so that the crew in the cockpit see a little of the light to let them know the lights are working, and to help them gauge how far the wing is out there when taxiing at night or dusk. On the Israeli C-47s (mallards), the plexiglass piece was shaped like a duck.