The helmets were taken after two vans were broken into in Meadow Croft on the Bilton estate during the early hours of Monday 10 December 2012.
Both helmets are brand new Airoh full face models, valued at around £200 each. One of them is described as white and red with skull graphics printed on the side.
Officers are appealing to anyone who witnessed any suspicious activity in the area at the time of the incident, or has been offered the helmets for sale, to get in touch.
Anyone who can help officers with their enquiries is urged to contact North Yorkshire Police on 101 – select option 2 – and ask for PC Raheel Akram or Harrogate police.
If you wish to remain anonymous, Crimestoppers can be contacted on 0800 555 111.
Please quote reference number 12120207869 when passing information about this incident.