Think of it as the Milo Yiannopoulos of coach vehicles.

For the past week, anti-transgender activists have toured the East Coast in a big, orange “Free Speech Bus.” Sponsored by the Spain-based advocacy group CitizenGo and several other conservative organizations, they’ve hopped from city to city to demonstrate against the notion that biological sex is different from gender identity.

“Boys are boys … and always will be. Girls are girls … and always will be,” reads a slogan emblazoned on the sides of the vehicle. “You can’t change sex. Respect all.”

Like Yiannopoulos — a former Breitbart News editor and right-wing agitator, not to mention critic of transgender rights — the Free Speech Bus is, by all appearances, there to provoke a reaction.

And it’s getting one.

The bus rolled into downtown Boston Wednesday morning, stopping first at the Massachusetts State House. About two dozen protesters were there waiting for it, holding signs and chanting, “No hate, no fear, trans people are welcome here!” as the Boston Globe reported.

Then the bus moved on to City Hall, where Democratic Mayor Marty Walsh, flanked by dozens of supporters, hoisted the transgender rights flag in opposition.

“We will not be intimidated by discrimination or harassment,’’ Walsh said. “And we will not tolerate these types of actions. When you deny the experience of transgender individuals, you are denying the experience of basic human civil rights.”

As the Free Speech Bus crawled through the city toward its third destination, Cambridge, Mass., protesters stood in front of it, blocking its path. At one point, someone lobbed a cup of coffee at the bus’s door, as local media reported.

Transgender advocates say a strong response is necessary in light of the threats the LGBT community faces on a daily bases.

“Words, in this setting, are violence,” Mason Dunn, a protest organizer, told the Globe. “We’re concerned about the health and wellness of our community.”

The bus’s organizers say they’ve come to expect such confrontation. If anything, the visit in Boston was relatively uneventful compared to the bus’s other stops.

The Free Speech Bus’s campaign started in Spain in response to a transgender rights pamphlet that featured an illustration of a boy with female genitalia and a girl with a penis. Beneath the image, a phrase in Spanish read “There are girls with penises and boys with vaginas. It’s that simple.”

Gregory Mertz, U.S. director of CitizenGo, said the organization brought the tour to the United States to demonstrate against policies that accommodate transgender people.

“There’s an agenda and movement that’s saying it’s okay for a boy to be a girl and that you can use whichever restroom you want,” Mertz told the Associated Press Wednesday. “We think that’s very harmful.”

(Advocates say views like this misrepresent their goals. Measures seeking equal bathroom access, for example, are intended to allow people to use bathrooms that correspond with their gender identity, rather than the sex on their birth certificate.)

Given the heated debate over transgender rights playing out in the country, Free Speech Bus organizers said they were preparing for conflict on their U.S. tour.

“We don’t know what the response to the #FreeSpeechBus will be in the US, but we expect that radical gender ideologues may try to get our bus shut down,” they said in a post on CitizenGo’s website. “Whatever happens over the next few days, we will not give into the pressure to stop this important campaign.”

The bus arrived in New York on March 22, stopping at Times Square, Trump Tower and the Stonewall Inn, the Manhattan bar that was the site of the 1969 riots by members of the city’s gay community. LGBT advocacy groups turned out in protest, condemning it as the “hate bus,” as USA Today reported.

The following day, after parking in front of the United Nations headquarters, protesters vandalized the bus, spray painting it with graffiti reading “trans rights” and smashing its front window.

After spending a couple days out of commission, the bus traveled to New England. It skipped a stop in New Haven, Conn., but a group of demonstrators held a rally against it anyway, erecting banners that read, “Every breath a trans person takes is an act of revolution.,” as the New Haven Independent reported.

The Free Speech Bus is now headed south, with stops planned in New Haven, Philadelphia, and Baltimore in the coming week. It’s expected to arrive in Washington on April 3, organizers say.

Opposition to the bus hasn’t been limited to on-site protests. The California game developer Aquma recently released an online video game that allows Free Speech Bus opponents to fight the anti-transgender campaign in the virtual world, as Vocativ reported. In “Ignorance Fighter II” — based off the classic martial arts game “Street Fighter II” — players can punch and kick a rendering of the Free Speech Bus until the tires and windows fall off.

When players succeed, an admonition appears on the screen: “Go rethink your bigoted beliefs. Gender identity is separate from biological sex.”

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