How do we decide what the “Don’t Tread on Me” flag, or indeed any symbol, really means? Photograph by Drew Angerer / The New York Times / Redux

In January of 2014, an African-American maintenance mechanic for the United States Postal Service in Denver filed a complaint charging that he had been subjected to racial discrimination. Specifically, as a recent Equal Employment Opportunity Commission filing on the matter put it, one of the man’s co-workers “repeatedly wore a cap to work with an insignia of the Gadsden Flag.” The cap design in question involves a coiled rattlesnake over the phrase “DON’T TREAD ON ME,” against a yellow background. You’ve seen it.

The Postal Service dismissed the complaint. But, this summer, that decision was reversed by the E.E.O.C., which, after some procedural back-and-forth, ordered the agency to investigate the matter. Eugene Volokh, a professor at the U.C.L.A. School of Law, brought this to the public’s attention through the Volokh Conspiracy, his legal-affairs blog on the Washington Post’s Web site. Observers of a particular ideological bent reacted with alarm or outrage: “Is the Gadsden Flag Racist?,” “Government Ruling: Wearing ‘Don’t Tread on Me’ Gadsden Flag Can Be Racist & ‘Racial Harassment,’ ” “Obama Administration: ‘Don't Tread on Me’ Clothes Are Racist,” and so on.

There was no such definitive “ruling,” from the Obama Administration or anyone else. The E.E.O.C. (which whipped up a dedicated page to correct misreporting around “the Gadsden Flag case”) had merely told the Postal Service, in long-winded legal terms, to look into the complaint. But however cooked up the notion that there was some kind of federal crackdown on the design, the controversy does point to something real. In recent years, the Gadsden flag has become a favorite among Tea Party enthusiasts, Second Amendment zealots—really anyone who gets riled up by the idea of government overreach. It’s also been appropriated to promote U.S. Soccer and streetwear brands. And this reflects a deeper question, one that’s actually pretty compelling: How do we decide what the Gadsden flag, or indeed any symbol, really means?

One answer involves history. The Gadsden flag is one of at least three kinds of flags created by independence-minded colonists in the run-up to the Revolutionary War, according to the writer and historian Marc Leepson, the author of “Flag: An American Biography.” Liberty flags featured that word on a variety of backdrops; the Pine Tree flag floated the slogan “An Appeal To Heaven” over a depiction of a pine tree. Neither endured like the design of Christopher Gadsden, a Charleston-born brigadier general in the Continental Army. His was by far the coolest, with its menacing rattler and provocative slogan.

The snake, it turns out, was something of a Colonial-era meme, evidently originated by Benjamin Franklin. In 1751, Franklin made the satirical suggestion that the colonies might repay the Crown for shipping convicts to America by distributing rattlesnakes around England, “particularly in the Gardens of the Prime Ministers, the Lords of Trade and Members of Parliament; for to them we are most particularly obliged.” Later, in what may be America’s first-ever political cartoon, Franklin published the famous “Join or Die” image, which depicts the American colonies as segments of a snake. Among other borrowers, Paul Revere put the snake in a seventeen-seventies newspaper nameplate. Gadsden’s venomous remix, for a flag used by Continental sailors, depicted the reassembled rattler as a righteous threat to trampling imperialism. “The origins of ‘Don’t Tread On Me,’ ” Leepson summarizes, “were completely, one hundred percent anti-British, and pro-revolution.” Indeed, that E.E.O.C. directive agrees, “It is clear that the Gadsden Flag originated in the Revolutionary War in a non-racial context.”

And yet, no symbolic meaning is locked in time. At the risk of proving Godwin’s law (which holds that all online debates work their way to some invocation of Nazis), consider the swastika. A symbol of well-being associated with Buddhists for thousands of years, it was used by commercial brands and even occasionally adorned U.S. and British military aircraft before the Second World War. But the Nazi regime’s black, white, and red treatment, and its association with anti-Semitism, violence, aggression, hatred, and death, obliterated the design’s earlier meaning in the West and beyond.

The shift in the swastika’s meaning is, in some ways, an outlier: there’s no disputing its ugly symbolism today. (It would likely not be difficult for, say, a Jewish worker to convince the E.E.O.C. that a colleague’s insistence on wearing a swastika cap was evidence of harassment.) Other symbols suggest the fluidity and ambiguity of meaning—and the underground, almost in-group messaging symbols can send. In the early nineteen-nineties, the Los Angeles Raiders logo (now the Oakland Raiders), which involves an eye-patched football player and crossed swords, had supposedly been so widely adopted by “street gangs” that many schools in the Western U.S. banned it because of “the connection between Raiders gear and gang activity,” according to a Times article from that era. More recently, a cartoon character called Pepe the Frog, invented by the artist Matt Furie as a kind of slacker humanoid amphibian back in 2005, has been repurposed in shadowy corners of the Internet—maybe ironically, maybe not—as a winky symbol of white nationalism. “Pepe can be used by the alt-right to slyly say ‘I’m one of you,’ ” Motherboard explained after Donald Trump, Jr., shared a Pepe meme on Instagram earlier this month, and a surprising number of reports, as well as the Hillary Clinton campaign, agreed.

As for Gadsden’s creation: after the Stars and Stripes was adopted as the official flag of the United States (with little fanfare or recorded debate, Leepson notes), the Gadsden design remained something of a Revolutionary relic for many years. By the nineteen-seventies, it had some popularity in Libertarian circles, as a symbol of ideological enthusiasm for minimal government and the rights of individuals; there was little mainstream interest in the flag as late as the summer of 2001, when Chris Whitten, who described himself in an e-mail as having “a background in the broader Libertarian movement,” started a Web site dedicated to the history of the flag (and associated merch). Traffic spiked after the September 11th terrorist attacks, Whitten says, and searches (and sales) also climbed as the Tea Party movement emerged. The symbol’s appeal spread through pop culture, as an all-purpose signifier of swaggering defiance. In 2014, Alabama became the seventh state to approve a specialty license plate with a Gadsden design.

Along the way, it picked up other connotations: strident anti-government sentiment, often directed with particular vehemence at the first African-American President. As the E.E.O.C. gingerly suggested, the symbol is now “sometimes interpreted to convey racially-tinged messages in some contexts,” citing the flag’s removal from a New Haven fire station after a black firefighter complained, and a 2014 incident in which two Las Vegas police officers were killed and their bodies covered by the flag. (The officers were white, but the shooters reportedly “spoke of white supremacy” and “the start of a revolution,” and were presumably sending that message with the flag.) Other skirmishes around the flag’s display, largely centered on its association with the Tea Party, have entangled small businesses, homeowners’ associations, and even an empty building. “People who collect historical flags like to fly them occasionally,” John M. Hartvigsen, president of the North American Vexillological Association, says. But some have shied away from “historical display” of the Gadsden flag because “it can now communicate a political sentiment that may not be theirs.”