Per the website advisorperspectives.com, at the beginning of this month the ratio result (129.8) was almost at its highest point in history, second only to its level (136.5) at the end of the dotcom bubble, just prior to big market drops in 2000 and 2002, and substantially higher even than just prior to the 2008 financial meltdown (104.9), which also, of course, saw large stock market losses.
Per the website gurufocus.com, which is updated daily, the U.S. stock market is significantly overvalued and, as of 8/19/17, the ratio stood at 130.8. This site also uses the ratio to forecast estimated total returns. It predicts that investments made today will, even including dividends, over the next few years provide the average investor with a lot more losses than gains.
Based on Buffett's preferred way of assessing these things, this is probably not a good time to be doing new investing. Indeed, investors might be better off gradually selling existing holdings to raise cash, against the possibility of buying more shares once the market takes a big hit, as overall it tends to do around every 4 years or so.