While it's impossible to predict the future or even identify market tops, there are a number of troubling signs that suggest stocks are too high. I discuss three of these in the video below, including the absolute level of the S&P 500 (^GSPC 0.95%), valuation expansion over the last year, and the overexuberance of investors in the recent IPOs of Potbelly (NASDAQ: PBPB) and Noodles & Co. (NASDAQ: NDLS).