“Investors” are so desperate to hold on to short-term paper that they paid $100 for a 3-month Treasury-bill at today's auction. That is a 0% yield – for the first time ever – lower even than the auction right after Lehman's bankruptcy in Nov 2008.
Chart: Bloomberg
It is probably safe to say that NIRP next, followed by more negative yields further to the right as the US gradually becomes Europe.