Police are on the lookout for two men seen on CCTV spraypainting obscenities on Castle Hill police station on Saturday.
Police say a woman saw two men spraying the building with blue paint about 10.55pm and called the police.
The obscenities on the wall were directed at the police.
The men fled on foot up Castle Street, towards Old Northern Road. Police believe they also sprayed graffiti on Castle Towers.
One man was described as wearing a black hoodie, white runners and dark clothing. The other man wore blue jeans and a purple hooded jacket.