MILPITAS – As billboard ads go, it isn’t splashy — just four words on a digital sign near an industrial stretch of I-880 in the East Bay: “Elon: Please Dump Trump.”

It flashes to traffic heading both ways on the interstate, just three miles from the Tesla factory. So far, no one is taking credit for the advertisement, which carries the tagline “Resist.”

Critics have targeted Tesla CEO Elon Musk for joining President Donald Trump’s business advisory panel, even as other tech company executives like Facebook’s Mark Zuckerberg and Uber’s Travis Kalanick have shied away from the Republican leader.

Musk returned to Washington, D.C. Wednesday to discuss infrastructure projects with the president. The tech mogul defended his decision to stick with the administration as an adviser in February, after Trump’s first travel ban.

“Advisory councils simply provide advice and attending does not mean that I agree with actions by the Administration,” Musk said in a statement. “I believe at this time that engaging on critical issues will on balance serve the greater good.”

Musk also said he’s been able to shape the council’s agenda, bringing forward discussions on immigration and climate change.

“I believe this is doing good, so will remain on council & keep at it,” Musk tweeted. “Doing otherwise would be wrong.”

The “Dump Trump” ad is posted near the Dixon Landing Road exit of I-880 — seen by as many as 211,000 drivers every day, according to CalTrans data. It’s been up for at least a week.

The advertisement carries a disclaimer that the message does not reflect the views of the billboard’s owner, Clear Channel Outdoor. The advertising company charges about $5,000 per month for a spot on a digital display board in the Bay Area, depending on how many ads share the digital space. Efforts to reach the ad’s sponsor through Clear Channel Outdoor were unsuccessful.

A Clear Channel spokesman declined to comment on the contents of the billboard. A Tesla spokesman referred to Musk’s earlier comments about his role on the president’s advisory board.

Other Silicon Valley leaders have kept their distance from Trump, who lost the state by 4.2 million votes. Rancor toward Trump in Silicon Valley has grown as the administration threatens to crack down on immigration and travel.

Larry Gerston, professor emeritus of political science at San Jose State University, said Musk has to consider the risks his companies, particularly Space X, face if he alienates the president.

“Think of the millions of dollars he’s getting from NASA to develop Space X,” Gerston said. “These guys are heavily subsidized.”

Public campaigns against companies are nothing new, he said. For example, protesters have waged attacks against Koch Industries, led by conservative brothers Charles and David Koch, and the Walton family, heirs to the Walmart fortune.

Musk, a clean-energy evangelist, has been targeted by oil and gas supporters, but the polite new critique appears to come from the left.

Gerston said companies need to calculate the hazards when crossing into the political realm.

“There is this thing in life,” he said, “called ‘self-interest’.”