In a year that has seen digital currency prices go higher not by percentages but multiples, investors are starting to worry that things have gone a bit too far.

is now considered the "most crowded trade," as measured by sentiment in the monthly global Bank of America Merrill Lynch Fund Managers survey. That means investors believe there are too many people on one side of the trade and it could be due for a reversal.

Bitcoin's price has surged about 330 percent this year, the beneficiary of a jump in interest for the cryptocurrency and a growing field of competitors, as well as a flight to alternative assets and, some fear, a speculative bubble.

The Merrill survey is one of the most followed and respected on Wall Street. Conducted during the week that ended Thursday, more than 200 global fund managers with at least $600 billion under management were surveyed.

Of course, a crowded trade doesn't have to mean it's nearing an end.