The Nasdaq composite is on pace for a record-setting month.
The technology-dominated index has closed positive in 15 of the 18 trading days so far this month; if that pace continues, May would mark the Nasdaq's winningest month since September 1996, according to Bespoke Investment Group.
The index, which hit a new all-time high in early Thursday trading, has advanced more than 2 percent so far this month and more than 15 percent so far this year. By contrast, in September 1996, the Nasdaq rose by 7.5 percent.
More from CNBC:
The recent collection of positive days is flashing a sort of contrarian signal, said Boris Schlossberg, managing director of foreign exchange strategy at BK Asset Management. While he would not bet against the index, he suggested trimming one's holdings at these levels.
"Typically, when you have that kind of concentration of positive days, mean reversion is about to kick in. So I think it could be a situation where 'sell in May' could be the best prescription for the Nasdaq," he said Wednesday on CNBC's "Trading Nation."
"Come out at of top and come back in September, November, when things re-rally," Schlosberg said.
Of course, 1996 was the year then-Federal Reserve Chairman Alan Greenspan wondered about "irrational exuberance" and whether stocks were reaching unsustainable heights. That was before the tech bubble got blown to a staggering level, which was of course followed by a massive crash.
This period looks significantly different, according to the strategist.
"There's no doubt that, fundamentally, all the tech companies have certainly come to the forefront. They are now the dominant companies in American industry — but that story has been really well told. I think profit-taking is due here, and I would be very cautious at trying to get long here at these levels," Schlossberg said.
On a technical basis, the index appears quite strong, said Craig Johnson, chief market technician at Piper Jaffray.
"The trend, by all definition, is our friend at this point in time. And we don't have any indication of a trend change happening here," he said Wednesday on "Trading Nation."
"I'm not going to fight the earnings trend of the market. We are finally seeing a lot of these names inside of the tech sector doing well."
Some of the tech stocks also remain supported from a fundamental perspective, Johnson added.