A number plate was stolen from a Vauxhall Astra parked in Church Lane, Harrington, before being dumped in a pub car park.
Police are appealing for witnesses to the theft which took place between midnight and 7am on Thursday, April 25.
A police spokesman said: “The rear number plate was taken from the vehicle and was later found in the car park of the Tollemache pub in High Street, Harrington.
“We would like to hear from anybody who saw the number plate being removed, or saw it being placed in the pub car park.”
Witnesses to this incident, or anyone with information about it, can call Northamptonshire Police on 101 or information can be given anonymously to Crimestoppers on 0800 555111.