The school's compliance office investigated the autographs, decided Lee did not receive payment, and cleared him of any wrongdoing.
"Last January, Marqise and other college football award winners were in Miami to be honored by the Orange Bowl Committee at the BCS Championship Game," USC's vice president of compliance, Dave Roberts, said in a statement. "While there, Lee signed several photographs, some that were personalized, for an individual who represented himself as a fan and collector."
USC also said it will send a cease-and-desist letter to the person selling Lee's autographs.
"I believed that the individual who asked me to sign the photos was a fan and collector. I did not ask to be paid, I was not offered anything, I did not get anything and I did not authorize my autographs to be sold," Lee said in a statement.
Lee won the Biletnikoff Award last season as the nation's top receiver.