Police are investigating after drivers on I-75 in Auburn Hills, Michigan, saw a pornographic video playing on an electronic billboard Saturday night.

Motorists began calling the Auburn Hills Police Department about the graphic images around 11 p.m., prompting police to dispatch a few officers to the scene to check it out and contact the people behind the billboard to shut it down, the Detroit Free Press reported.

“It was very bizarre,” Chuck McMahon told WDIV. “I thought maybe it was a billboard for a strip club or something.”

Auburn Hills Police Lt. Ryan Gagnon said the videos had been circulating for 15-20 minutes.

The company in charge of the billboard, Outfront Media, took down the electronic billboard once it found out what was playing. But the company told WXYZ Detroit that it was not their billboard.

It is unclear how many people witnessed the billboard, or if any children witnessed what was going on.

Police are investigating if someone hacked the billboard, and how the obscene images ended up on a billboard placed on a major freeway.

Hackers have gotten creative with road signs lately. In Seattle, a hacker broke the code of an electronic road sign on Wednesday to make the message read, “Impeach the bastard.”