But as far as I know, the coins issued by MLM firms are not traded in stock markets. Are there any MLM companies traded on stock exchanges?
Are you talking about big multibillion dollar MLM companies, which are fully legit and grown to the point of having shares traded on an stock exchanges?
Because there are many: Avon, Herbalife, Natura Cosmeticos, Tupperware Brands Corporation and some more.
If you asked about MLM companies which issue their own 'private' currency.
Then no, it is worthless IMO. I don't think it has any value and is recognized by anyone else beside these companies.