The image of O'Pake's name and face spraypainted was posted to the Schuylkill County Democratic Committee's Facebook page on Thursday.
The billboard is located along Route 54 between Mahanoy City and Interstate 81 on the Vulcan Hill.
"It's disheartening" said O'Pake. "My supporters put a lot of time, work, and money into this campaign".
"No one should try to influence the election in a negative way".
The incident is being investigated by police.
Both candidates have reported their smaller signs being vandalized in other incidents as well.