Warren Buffett’s house—the same one he has lived in since 1958—is famously nondescript.

The world’s sixth richest man lives in a pretty ordinary single-family home on a corner lot in suburban Omaha. A millionaire could afford it, and an oligarch or British prince would turn his nose up at it. Mr. Buffett is worth $145 billion.

What is noticeable, though, is the absence of a “blue dot” sign on the lawn out front. In the affluent neighborhood of Dundee, where Mr. Buffett lives, almost every house has a white sign outside with a circle a foot wide painted blue at its center. 

The blue dot, which started as a grassroots campaign to signify support for Kamala Harris, has sprouted all over Omaha and—incredible as it seems—might just deliver her to the White House.