My first thought. Another possibly died in Ukraine?
"What is the meaning of the "Z" symbol?
According to Galina Starovoitova Fellow Kamil Galeev, "Z" is a letter that Russian Military are putting on their vehicles departing to Ukraine. "Some interpret "Z" as "Za pobedy" (for victory). Others - as "Zapad" (West),” the scholar said on Twitter."
I'm guessing he will be moving Twitter HQ out of San Francisco.