What happened

After heading lower earlier this week, shares of Alphabet (GOOGL 10.22%) (GOOG 9.96%) moved higher on Thursday. As of 2:16 p.m. ET, the stock was up by 4.3%.

The catalyst that appears to have boosted the tech giant was a robust quarterly report from rival digital advertiser Meta Platforms (META 0.43%), which provided further evidence that the ad market may be on the mend.

So what

After the market close on Wednesday, FAANG stock Meta Platforms (META 0.43%) ended its streak of three successive quarters of declining ad sales with a remarkable rebound. First-quarter revenue climbed 3% year over year to $28.6 billion, its first quarter of growth since Q1 of last year.

Those upbeat results came on the heels of Alphabet's own return to growth. Alphabet's revenue increased by 3% in the first quarter to $69.8 billion, though part of that rebound was attributable to the strong performance of Google Cloud.

Roku (ROKU -10.29%) also delivered better than expected first-quarter results this week, returning to growth after its revenue was flat year over year in the fourth quarter.

Alphabet and Meta are the biggest names in digital advertising, and Roku -- the largest aggregator of streaming services -- makes the lion's share of its revenue from the digital ads displayed on its platform. It is well documented that marketers tend to pull back on ad spending during challenging economic times, and that tendency has been evident in the recent financial results for this trio. That all three returned to top-line growth in the same quarter is the clearest sign yet in this cycle that the advertising market may have turned a corner.

Now what

To be sure, the economy is a complex system, and the current positive trend could reverse on a dime. The Federal Reserve has said it's expecting the U.S. to enter a mild recession later this year, and if that happens, businesses could respond by cutting back on ad spending yet again -- but any such pullback will likely be short-lived.

At the same time, Alphabet has dominating leads in both online search and digital advertising, and its stock, currently valued at 4 times next year's expected sales, is trading near a historically low valuation.

Investors who buy Alphabet stock now will likely be celebrating that decision three to five years down the road.