Getty Images Stocks and the VIX have moved in tandem of late.U.S. stocks and one popular measure of volatility on Wall Street have been moving in lockstep lately, and some market experts think that is an ominous sign. Indeed, the Dow Jones Industrial Average DJIA, -0.09% and the S&P 500 indexSPX, +0.01% are on pace to close out August higher, booking their third weekly gains in a row and the best August return in four years, while the Nasdaq Composite Index COMP, +0.26% was on track for its second weekly advance and its best month in 18 years, according to FactSet data. The problem? The Cboe Volatility Index VIX, -4.95% was producing even better returns, up 15% for the week and 7.5% in August thus far as the S&P 500 and the Nasdaq have mostly put in repeated records over the past several sessions.via