There is no specific Road Rule in NSW that states that you are not allowed to dip your lights to warn other road users that the police are ahead. However, you could receive an infringement if a police officer was to allege that while you were warning another driver, you are also likely to dazzle them.
NSW Road Rule 219 states a driver must not use, or allow to be used, any light fitted to or in the driver’s vehicle to dazzle, or in a way that is likely to dazzle, another road user. This type of offence can attract 1 demerit point and a $110 fine.
Another more specific Road Rule in NSW is Road Rule 218 which states:
The driver of a vehicle must not use the vehicle’s headlights on high-beam, or allow the vehicle’s headlights to be used on high-beam, if the driver is driving: (a) less than 200 metres behind a vehicle travelling in the same direction as the driver, or (b) less than 200 metres from an oncoming vehicle.
Both 218-1 (a) & (b) each attract 1 demerit point and a $110.00 fine. Once again, you could receive an infringement for breaching this rule while in the process of warning an approaching driver of a speed trap ahead.
Do you appreciate when other drivers give you a warning of police checkpoints ahead?