If insider selling is an indicator of the future direction of stock, then certain equities may soon be taking a bath.

As the stock market enjoyed its sharpest increase since 1938, a massive sell-off of stocks by executives and insiders of U.S. corporations followed in the wake of that upturn, according to Bloomberg.com.

Insiders sold off NYSE-listed stocks at a more than eight-to-one dollar ratio over what they bought, according to Washington Service, which tracks corporate insider stock transactions.

The same insider-selling ratio also hit the Standard & Poor's 500 Index, which soared an astounding 26 percent from its 12-year low on March 9, with some $353 million in shares being sold by the last week in April.

Insider selling ran at the highest level since October, 2007, when stock markets hit a high after a 17-month decline.

"They [insiders] should know more than outsiders would, so you can take it as a signal that there is something wrong if they're selling," William Stone, chief investment strategist at PNC Financial Services Group, told Bloomberg.

Despite these high levels of insider selling, SEC filings indicate that other insiders at other firms are now buying, and investors are mildly optimistic about the general direction of the stock market.

"In order to make everyone a believer in this rally and the market, lower volatility has to be sustained for 60 to 90 days," Randy Frederick, director of trading and derivatives for Charles Schwab, told The Wall Street Journal.