The man, aged 20, sprayed four Cyrillic letters S, which stands for "Only Unity Saves the Serbs", and "Serbia" on the monument in the night between May 6 and 7.
The monument was erected in tribute to 12 policemen who had been killed in an ambush by Serb paramilitaries in Borovo on May 2, 1991.
The police said they would press charges with the municipal prosecutor's office for juvenile offences.