Deputies arrived at a tow yard at about 1 a.m. Saturday in the 7100 block of Mission Boulevard near the 60 Freeway and found two men behind a locked gate. Authorities said one of the men was injured after he reportedly fell off the billboard and landed on the hood of a car.
Fresh paint was found on the billboard and a can of spray paint was found at the scene.
Deputies believe the injured man, 18-year-old Eric Jimenez, strapped himself to the sign to allow him to spray paint it. The strap evidently became loose, causing Jimenez to fall.
The accomplice, identified as 18-year-old Anthony Michael Lobianco, was apparently working as a lookout.
Jimenez was taken to a hospital for treatment and charges against him were pending, deputies said.
Lobianco was booked for suspicion of felony vandalism and conspiracy at the Robert Presley Detention Center in Riverside.
City News Service contributed to this report.