"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.