Oh, I forgot... SKEW

SKEW is the CBOE indicator that tries to put a probability on an improbable event, specifically a market crash or what is called a "Black Swan". $115 is the normal range for SKEW, right now it is elevated which increases the chances, past crashes have been in the $140-$145 area, but what is notable is not the reading, but the rate of change to the upside in SKEW and that it is moving up.

 This daily chart shows the Rate of Change which has been higher recently, more so than the rest of the year. Sometimes it's easier to see without the indicator.

SKEW at $126.73