Given the offbeat sense of humor that Mr. Musk has sometimes displayed in his Twitter posts, there was immediate speculation that the $420 figure was a reference to a widely used numerical code — 420 — that refers to marijuana. (April 20, 4/20, is celebrated by some people as a kind of national marijuana holiday.)

Tesla, whose shares Nasdaq halted trading in for much of Tuesday afternoon, was silent on the subject of Mr. Musk’s Twitter post for more than two hours. Around 3:30 p.m., the company published an email from Mr. Musk to employees that said, “I’m considering” taking Tesla private, while adding that “a final decision has not yet been made.”

But it was Mr. Musk’s “funding secured” statement on Twitter that may put the iconoclastic founder most at risk. He provided no details about how much funding had been secured, from whom or under what conditions. His email to employees did not mention anything about the funding.

“That’s a clear factual statement,” said John C. Coffee Jr., a professor at Columbia Law School who specializes in corporate law and securities fraud. “If it’s not fully secure, that’s potentially a very material misrepresentation, and a very straightforward violation of Rule 10b-5” of the securities law — in short, securities fraud.