This might not be of much interest to buyers of global equity markets at this point, but it is signalling ominous signs of growing funding stress in the financial "plumbing".
As Bloomberg notes "cross-currency basis swaps, which money managers and corporate treasurers outside the U.S. can use to borrow in dollars, remain close to the widest levels since January even after quarter-end, when such financing strains typically dissipate. The market was a key indicator of stress during the financial crisis, and while it's nowhere near the alarming levels of that era, it's still garnering the attention of analysts."
The shortage in Europe is the worst since the EU Crisis and the shortage in UK is the worst since Lehman as Japanese dollar shortage is extreme too.
In simple terms, the CCBS is the cost in basis points (typically for three months) of swapping these currencies into dollars over and above prevailing interest rate differentials. In a benign environment the CCBS should trade at zero, not in negative territory. The latter implies a shortage of US dollar balance sheet (credit) offered by the global banking system.