Another member recently asked the same question about his made-in-England Summit slot.
A couple of possibilities come to mind:
1. Many offshore manufacturers tried to get in on the US market; as you know, a few were reasonably successful.
2. The $ before the number, and cent-mark after it, are also used in Canada and Australia.
3. I have seen US-coinage slot machines on non-US cruise ships, and in a few Caribbean resorts for US tourists.
If you can, post some inside-pictures, and the label. They will add to the interest, and perhaps we can help.