Guernsey Police is investigating the incident, which occurred sometime between 15:00 and 19:30 on Thursday 22 July.
It is suspected the damage has been caused by a third vehicle colliding with the two parked vehicles before leaving the area.
Anyone who saw what happened or has any other information is asked to contact PC 138 Falla on 222 222.
Alternatively, they can contact CrimeStoppers anonymously on 0800 555 111.