Thames Valley Police has launched an appeal for witnesses to the incident.
The incident happened between Friday September 24 and Tuesday September 28, when the Pride flag displayed at Bicester Fire Station, Queens Avenue, was damaged with homophobic graffiti.
Investigating officer, PC Phil Morris, based at Banbury police station, said: “I am appealing to anyone who may have witnessed this incident, or has information about what happened, to please come forward.
“Anyone with information can contact Thames Valley Police by calling 101 or making a report online, quoting reference 43210441417.
“Alternatively, if you wish to remain anonymous, you can contact the independent charity Crimestoppers on 0800 555 111.”