SAN FRANCISCO – Owners of the Giants baseball team have never struck me as stupid — greedy, perhaps, since they shamelessly sell a bottle of Bud for eight times what it’s worth, but not stupid.

So, when they announced the other day that they have accepted a reported $20 million annually to change the name of their stadium for the fourth time in less than 20 years, I figured they must know what they’re doing.

The Giants, like virtually every sports franchise in the nation, are cashing in on corporate vanity. Flush with cash thanks to Trump economics, companies are spending unprecedented sums to place their names on sports venues, despite growing evidence that playing this name game has little measurable value.

When the Giants opened their stadium in 2000 it was known as Pacific Bell Park. A few years later, the name changed to SBC Park, and then to AT&T Park. Now, it’s Oracle Park.

The Bay Area tech giant suffered ego damage when it lost out on naming rights to the basketball arena where the Warriors play. The Oracle name has been on the venue in neighboring Oakland since 2006, but the Warriors are moving to a new facility in San Francisco, branded Chase Center, for which JPMorgan Chase paid an estimated $200 million. Oracle quickly agreed to pay a similar sum to the Giants, whose fans already suffer naming fatigue.

For their first 35 years in San Francisco, the Giants were happily ensconced at Candlestick Park, named for the finger of land on which it was built. In 1995 naming rights were purchased by 3Com Corporation and Candlestick became 3Com Park. After the Giants moved out the rights were sold to Monster Cable, a maker of electric cables, and 3Com became Monster Park. Enraged San Franciscans voted to require that the name be legally changed back to Candlestick as soon as Monster’s contract expired.

The stadium’s football tenant, the 49ers, moved to a new facility in Santa Clara, for which Levi Strauss paid $220 million for the right to call it Levi’s Stadium — or, as sportscaster Chris Berman dubbed it, The Big Bellbottom.

Corporate naming can be traced back to 1921 when chewing gum magnate William Wrigley Jr. purchased the Chicago Cubs. Six years later Wrigley put his name on the iconic Addison Street stadium, and the rest is history.

Today, just about every pro sports venue bears a corporate name. Notable exceptions are Fenway Park, named after its Boston neighborhood, New York’s Madison Square Garden, named after a president, and Lambeau Field in Wisconsin, whose name honors the beloved football player and coach Curly Lambeau.

Daniel Rascher, who examined 85 North American naming-rights deals, estimates that if a team had three losing seasons, the value of its naming deal dropped by 5 to 7 percent.

Research by Sports Market Analytics found that among the three major pro sports — baseball, football and basketball — over half the fans indicated that a venue’s sponsorship had no influence whatsoever on their purchase of the sponsor’s product or service.

How could it, when some venues change names as quickly as their teams change players? Consider the place where the NFL’s Chargers play in Carson, Calif. Known as recently as 2012 as the Home Depot Center, it next became the StubHub Center, and is currently called Dignity Health Sports Park.

Enter a wireless company called Rokit. For the season just ended, the company arranged to buy naming rights to the playing field, while Dignity Health’s name was on the stadium itself. It’s called Rokit Field at Dignity Health Sports Park.

Meanwhile, the Giants, shrewdly managed to sell naming rights to the broadcast booth inside what is now known as Oracle Park to Hawaiian Airlines.

As P.T. Barnum might have put it, there’s an egomaniacal corporate marketing exec with a checkbook born every minute.

Peter Funt is a writer and speaker. His book, “Cautiously Optimistic,” is available at Amazon.com and CandidCamera.com.