General Motors (GM -4.19%) just sounded a warning for the entire stock market.

The auto manufacturing giant released its first-quarter earnings on Tuesday morning, but said that it would delay its earnings call until Thursday, apparently waiting for some clarity on tariffs. More importantly, it said that its guidance was no longer applicable due to tariffs and that it was suspending share buybacks.

GM's stock fell modestly on Tuesday, trading down between 1% and 2% for most of the session, even though its first-quarter results were solid. Revenue in the quarter rose 2.3% to $44 billion, which was ahead of the consensus of $43.2 billion.

On the bottom line, its adjusted earnings per share rose 6% to $2.78, which edged out expectations for $2.66. The company also said it would raise its quarterly dividend from $0.12 to $0.15 per share.

GM is the first of the major domestic automakers to report earnings, so it's not surprising to see it react to the uncertainty around the tariff situation by pulling its guidance and suspending share buybacks.

However, the news that the Chevy maker is suspending guidance seems to have taken the air out of the best reason to own the stock.

Image source: General Motors.

The GM bull thesis

For years, GM has been a market laggard. Though the company is a reliable profit generator, its growth is sluggish. Investors are fearful of disruption from electric and autonomous vehicles. And it has a capital-intensive, cyclical business at risk of a downturn. GM's bankruptcy during the great financial crisis was not that long ago, lingering in the memory of investors.

Because of those factors, the stock trades at a dirt-cheap valuation, similar to peers like Ford Motor Company and Stellantis. But there's a key difference between those two stocks and GM. Both Ford and Stellantis are dividend powerhouses, offering yields of 7.5% and 8.2%, respectively.

GM, on the other hand, currently pays a yield of just 1.3%, even after the dividend hike it just announced.

Low-valuation stocks are attractive in part because the math allows them to pay high dividend yields. Since the stocks trade at a low multiple of their profits, sharing their profits through dividends goes a long way.

There's another way that value stocks like GM can return capital to shareholders -- through share buybacks. Buying back stock doesn't reward investors directly like dividends, but it raises the business's per-share earnings by removing some shares from the equation. Share buybacks also become more valuable as the share count declines.

Historically, GM had a rewarding track record of buying back stock. As you can see in the chart below, GM has reduced shares outstanding by about a third over the last decade:

Data by YCharts.

What's next for GM

It's unclear at this point what the buyback suspension means; the company is likely to address it in more detail on the Thursday morning earnings call.

We don't know, for example, whether this is just a temporary measure while tariffs are being negotiated, or if it's something more sustained -- GM could be protecting its cash ahead of a potential recession.

For investors, however, a multiyear suspension in share buybacks would dampen much of the bull case for the stock. And it would signal that the company isn't confident in its ability to generate a profit in the current economy.

Ironically, GM's announcement comes shortly after it decided to disband Cruise, its loss-generating autonomous-vehicle subsidiary. It should have had even more firepower to spend on share buybacks.

Uncertainty reigns for now, especially with the earnings call still pending. But without a more detailed explanation, a pause on share buybacks looks like a clear bearish signal for the stock.