Are popular crypto stablecoins the next subprime CDOs, or even outright Ponzi schemes?The settlement agreement between Tether and the New York Attorney General's Office, court transcripts, skimpy disclosures, and independent analysis by Bloomberg of Tether's financials paint a troubling picture.Two stablecoins, Tether and USCoin, now have around $100 billion total in market cap and may not be backed by adequate collateral, or in Tether's case, much collateral at all.Tether is particularly sketchy. I believe there are some obvious red flags worth noting about the coin.The craziest one? Tether supposedly owns 5 percent of the world's commercial paper, but no one can seem to find anyone who has done business with them.