The could make a really big move higher if the index were to close two Fridays in a row above 2,135, BTIG's chief technical strategist told CNBC on Monday.
"For me, it's very important not to see just see a little inch above that, but a confirmation of a breakout," Katie Stockton said, acknowledging the resistance that's been seen around 2,100. "That's saved me ... to avoid these false breakouts."
The S&P 500 opened in record territory on Monday, eclipsing its May 2015 intraday close of 2,134.72. The index surged 1.5 percent on Friday, just shy of that level, on the stronger-than-expected June jobs report.
"I want to see consecutive Fridays, so two weekly closes in the S&P 500, above that 2,135 level. That would convince me that we've broken out," even with summer's traditional light trading volume, Stockton said on "Squawk Box."
"Then we can arrive at some pretty impressive upside targets," she added. She predicted a 12 percent move to 2,400 could be in the cards.
As for the Dow Jones industrial average, it, too, rallied sharply higher at Monday's open, but remained about 100 points away from its intraday record of 18,351.36 in May 2015.
Year to date, the Dow and the S&P have virtually mirrored each other — plunging at the start of 2016 before bottoming for the year on Feb. 11. The market's march higher was then temporarily detoured last month after Britain's vote to leave the European Union.
Dow theorists like to see moves in the industrials confirmed by the transports. But that hasn't happened yet.
In fact, the Dow transports made lower lows after the Brexit vote and failed to keep pace, up only about 3 percent for the year, compared to the 4 percent-plus moves for the S&P and the Dow industrials.
"The [Dow] transports have underperformed up until last week. So last week, we saw some more offensive positioning and that would [also] be bullish if it persists," Stockton said.