So I have certainly made investments in countries with crisis markets, and I'm getting a little better at it than I used to be, because I have had more experience now. That's why I keep emphasizing that you have to know what you're doing. And by that I mean paying attention to and doing your homework on a stock or a commodity or a country. If you do that with a crisis market, then chances are you can move in and make some money.
It's illegal for Americans to invest in North Korea. It's probably illegal for us to even say the word "North Korea". I look around to see which countries are hated. In North Korea there is no stock market, and there is no way to invest, especially if you are an American, but sometimes you can find something in a secondary market.
Stamps and coins were the only ways I knew of that one could get some sort of exposure. This is because you are not investing in the country, obviously, because you are buying them in a secondary or tertiary market. That said, I think the US government is going to make owning stamps illegal too.
There were people once upon a time—and maybe even now—who invested in North Korean debt. I have not done that, but it may be another way that people can invest in North Korea. I don't even know if North Korean debt still trades, but it was defaulted on at some point.