The
Wikipedia article on Gun Money is a reasonable summary of the coinage issue. There are several examples on the forum, too, like
this one with my August 1689 halfcrown; do a forum search for "gun money" to find the others.
They are not "counterfeits", in the usual sense of that word. They were issued by James II after he fled England and tried to raise a loyal army in Ireland. He was broke, so he issued this token coinage, made from scrapped cannons, old church bells or anything else brassy that came to hand, under the promise that when he regained the throne, the tokens would be exchanged 1 for 1 with good English silver coin.
Gun money is dated by month as well as year of issue. Your coin is a halfcrown ("XXX" means 30 pence, or 2 shillings sixpence) dated September 1689. This, in theory, would have allowed the earlier dated tokens to be given first priority of redemption. Since James II never regained the throne, the matter of redemption never came up.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis