I was looking at a few of the rifles the other day and picked up a British "Made in Great Britain" Diana 25. It has the 2 holes in the cylinder for the scope rail.
What struck me as odd on the LHS of the breech block it has J and 6 numbers. Was the J to show it was below a certain power level for foreign markets? And 6 numbers?

I've not seen this on another DIana 25. Any thoughts?