The billboards read, "VOTER FRAUD IS A FELONY" and were set up this month in largely poor, minority neighborhoods in Cleveland, Cincinnati, Columbus, and Milwaukee.
Clear Channel Outdoor and Norton Outdoor Advertising said the buyers were anonymous, and would not reveal their names.
But an African-American news division of NBC, called TheGrio and activist group, One Wisconsin Now, learned Milwaukee residents Stephen and Nancy Einhorn bought the signs.
The couple has donated thousands of dollars to conservative candidates, political action groups, and the Republican National Committee…and serve on the boards of the Milwaukee Art Museum and Milwaukee Ballet, respectively.
Democratic State Senator Turner says she's seen philanthropists benefit worthy causes such as libraries and community centers…
"But never did I think philanthropists would use their money to inject fear into African-American, Hispanic, and poor communities, when it comes to voting," she says.
Turner says she still wonders how Clear Channel Outdoor allowed anonymous billboard purchases in 2010, as well as this year. Clear Channel said anonymous political advertising was a violation of company policy, when deciding to take down the "voter fraud" billboards last week.
In a statement, the Einhorns say they were doing a public service, since voter fraud "undermines democracy". Critics say actual cases of voter fraud are extremely rare, and the signs were more about voter intimidation.