Perhaps it could have been made in comemorance of June or in the month of June in the year 1947. Was it the only one you found or were there more? Try studying it carefully and see if you find anything distinctive about it. Look for any particular patterns or sigils on it.
If possible, try holding it while you meditate...feel its presence..."scan" it. Don't rush into it, just let your mind guide you. You might find out something interesting.
Afterwards, if you're still interested, try researching online about it by entering the details you find.
Good luck and blessed be.