While the famous Hindenburg dirigible crash took place in 1937, its financial namesake, the Hindenburg Omen, points to a time eight years earlier when the stock market crash ushered in the global depression.
This omen, which has foreseen stock market crashes on two separate occasions in the 21st century, made its appearance once again on May 31, and the Dow responded with a 207 point plunge over the course of three hours.
The Hindenburg Omen is a combination of technical factors that attempt to measure the health of the NYSE, and by extension, the stock market as a whole. The goal of the indicator is to signal increased probability of a stock market crash.
The rationale is that under "normal conditions" a substantial number of stocks may set either new annual highs or new annual lows, but not both at the same time. As a healthy market possesses a degree of uniformity, whether up or down, the simultaneous presence of many new highs and lows may signal trouble. - Wikipedia
...there appear to be three reasons being discussed for this drop in stocks.
Third, and perhaps more important to some, based on intraday data so far, the much-discussed Hindenburg Omen has been spotted (as it also was before QE2 was announced to save the world). The last time we were this high in stocks and the Hindenburg was spotted was October 2007... - Zerohedge
As the markets reached new all-time highs on a 7 month rally, only to fall to their worst two week drop in 2013, the omen known as Hindenburg is an ominous sign that the party of 1929, 1987, and 2007 may be over, and over quickly if the forecast holds true to historical trends.